Ok, so here's the big post I mentioned. It's gone under various revisions based on games I'm playing at the time in terms of inspiration. Just a disclaimer, I'm not a tournament Smash player, but I play other fighters mostly so you'll see lots of inspiration from there, but some mechanics like air dashes are found in games like Kingdom Hearts.
[COLLAPSE="Throws:"]
Gone: Pummeling
Reason: I never saw much value in it that wasn't the Ness/Lucas lock. Also, since the throws do less damage because of the pummels, it's probably just best to go back to just the throws. When to decide the direction is like Smash 64 but a little quicker.
New: Grab Breaks
Reason: Commonly known as tech grabs, this is the result of two characters try to grab each other at the same time (does not apply to special grabs which are random and port priority doesn't factor). When done, the two grabbers push each other away resetting the situation. This also gets rid of the notorious chain grabs.
New: Two grabs for tether users
Reason: Provide the tether users a quicker alternative. Do a neutral grab input like everyone else to get a normal grab. Do side+Grab for the tether input. Tether grabs cannot be grab breaked, but they can still be dodged.
Change: Throws only grab grounded characters.
Reason: Adds mixups on close range offense and can help prevent chain grabs. Also, certain command grabs are capable of grabbing airborne opponents (i.e. Koopa Klaw) and some characters will have air throws.[/COLLAPSE]
[COLLAPSE="Movement"]
Gone: Random Tripping
Reason: Do I need to explain this?
New: Air Dash
Reason: To provide new aerial mobility. Uses up one jump each time. To do it, do double tap forward or backward for the intended direction.
New: Turn-Around
Reason: Provide players the use of their BAirs while facing forward and brings back the old edgeguarding game without scrubbing it up. Can also be used to run away and be on the offensive at the same time. To do this, a half circle with the control stick from the direction you're facing to the other side.
Returning: Momentum
Reason: Smash needs to obey some laws of physics as Melee and (presumably) 64 did. To, say, go in the opposite direction, you must hold back for a specific length of time. This is so Turn-Around doesn't case momentum loss if practiced enough.
[/COLLAPSE]
[COLLAPSE="Defense"]
Change: How to block.
Reason: To provide a more in depth, yet more intuitive means of blocking and to also provide positioning based mixups.
The shield bubble is now reduced to somewhere 1/4 and 1/3 its original size. To change the position of the shield, move it with the control stick. As you can see, the shield will only cover part of your character's body. This allows for mixups based on hitbox and shield positioning, opening a wide array of tactics never seen in Smash.
Due to this change, the shield no longer shrinks over time. Rather, it develops a deeper shade of its color like Yoshi's shield. To roll or dodge out of the shield, you must double tap for the roll or dodge you want. This is to prevent accidental rolls or dodges while blocking or vice versa.
New: Move specific blockstun.
Reason: It just makes more sense really. Also adds a new sense of risk:reward.
New: Universal Counter
Reason: Provide some OOS/Out of Blocking options for each character. At the cost of some meter and pressing B while blocking as the hit lands, the blocker parries the attack and responds with some specific attack. Luigi could have his Tornado as an UC, for example.
Change: Hybrid Air Dodge
Reason: Compromise between the two air dodge versions. Neutral is limited to two dodges in the air while the other directions are limited to one and go into a helpless animation.
New: Aerial Ukemi
Reason: Brawl's air dodge basically allowed this at the expense of reducing hitstun. This seeks to fix this by making it where this done only at the end of the hitstun. Do a shield input and and hold, left, right, or neutral to recover in that direction. Some vulnerability is on the ukemi so this is where aerial mixups come into play. The initial part of the aerial ukemi has invincibility though.
Changed: DI streamlined to just SDI or at least a simplification of DI to just three options.
Reason: Always seemed more complicated to me than it should be.
Changed: SDI inputs.
SDI Inputs now just require one stick to specify a direction.
Reason: Why was it that we needed two sticks to give out one direction? That just makes things difficult for beginner players to get the hang of SDI.
To make things easier, there is a slightly longer freeze when attacks land than before. Logically, the length of the freeze would depend on the attack strength.
Change: SDI is only on specific attacks.
Reason: To encourage the player to decide between mixups and dealing certain damage. Also, to make mutli-hitting moves not so poor because they could be SDI on the first or second hit (i.e. Zelda's USmash). [/COLLAPSE]
[COLLAPSE="Attacks"]
New: IASA Frames on active frames
From the time an attack comes out until its recovery, the player can go from landing one attack to a jump, dash, air dash, special, normal, etc. depending on the move while on these frames. Where the IASA frames are depends on the attack, but most of your attacks will have their IASA frames specifically on the active frames.
Reason: Provides way more options for pressure, escaping, and keeping the flow of the match. Also increase the match's pace dramatically
New: Canned Combos
Reason: To encourage a stronger ground game. These combos work very similarly to Starfox Adventures' combat system, but further expanded on. You still have access to past attacks, but this opens up combo possibilities if explored enough to where you can juggle or link canned combos together. These chains may provide attacks and specials exclusive to a canned combo.
An example of a canned combo would be Link doing A > A > 3A which would be two swings and a swing on the head for a ground bounce. The number, length, and inputs of the canned combos would be determined on a case by case basis.
There are also aerial canned combos, but is not necessarily a universal feature.
New: Universal Smash Combo
Reason: Provides a universal flowchart/tree for all characters. The flowchart, at its basic level is this: Jabx1-3 > Tilt > Smash > Special. This also gives beginners an easy to do combo with enough different ways to do it. In the air, the universal Smash Chain is NAir > Direction Aerial of Choice > Special.
New: Counter Attacks
Reason: Higher risk, higher reward. Countering an attack leads to higher damage and longer hitstun or some property like crumbling for the first attack. Certain moves will have additional properties. PK Fire, for example, will have a burn effect lasting a few seconds if performed as a counter. Note, this mechanics does not apply for universal counters.
New: Smash Meter
Reason: Provide more options. Think of it working like MP in RPGs. The meter has many uses. It can be used for universal counters for 25% meter, super specials for 25%, super smashes (more on that later) for 50%, or final smashes for 100%.
New: Super Specials
Reason: Again, more options. By doing B+A+Input, you get a stronger version of special with new properties. Some of these might include invincible startup, ground bounce, projectile invulnerability, etc.
New: Super Smashes
Reason: Give us a more balanced super compared to Brawl's final smashes. These are your typical fighting game supers. They can be canceled on hit from specials or normals if the move you're comboing from allows it. The input for the Super Smash will depend on the character. Every Smash ball fills the meter by 50%
Change: Final Smash
Now they're more like fatalities minus the gore. Under certain condictions, you can end the match in a very flashy way with a cutscene and what not. Not the most practical mechanic, but a nice bit of fanservice. Final Smashes are doing with down,down,B+A. [/COLLAPSE]
Might update later.