One of your biggest problems is using silly mombo jumbo. If people can;t understand your ideas, then you wasted both of our time.Okay, I appreciate you showing me why that example of execution won't work for ground pound because you believe it won't feel right. However, Tap-Hold (Charging) is not relegated to simply charging anymore. Not in Brawl. Tap-Hold in A comboes and B moves also means continued use until button release.
With that given in Brawl, let's look at Ground Pound.
Ground Pound's physics is Mario slamming down from the air, and so holding down B is a representation of going from unpressed to pressed and held, as a pound does when he sits down. The hold part also simulates to a person that holding the button makes sense while Mario is in the process of going down. This is an alternative to using Thumb stick held Down (as DDD's Up B is held up.) Why an alternative? Because if not, then no other Down B move could co-exist as a tap b but hold down stick for DI. (ie using tornado and DI'ing down with it would be negated by facilitating Ground Pound with hold stick down rather than button)
He's in stun state from the impact (recovery frames) so a visual cue of the move being done allows you to see to let go of B by that time.
Consider the bold. That is, that holding the button continues the move until released (which has been present in Smash Brothers since, at the latest, Melee).
The problem is Mario is going to do a completely different moves when you hold the B button down longer. When you hold B for jigglypuff's rollout, she charges the attack. When you release the button, the move is "released." This is present in many games including Megaman and Metroid. This motion feels natural as the player understands that the move is stronger if you hold the button and when you release the button, the move comes out.
When the player holds down the button with Mario's Down B, he will immediately do a new attack. Your thinking in terms of ques, but players wont think like that. They will see the moves being like every other move, coming out on first press (holding is only for charge moves and this is intuitive as it's in a bunch of games). This would be in contrast to every move in the game.
The other problem is that what is going to be the hold down time? It works for Quick Draw, Headbutt and Roll Out because if you tap it, it still works, and if you hold it slightly longer then it comes out (just not as fast). In this scenario, if you hold it slightly longer, you are no longer doing Fludd (or Mario Tornado) but a different move all together.
The problem is you are taking your idea and say "Oh, golly yes it will work." Note how what you said is the same thing just edited to add what I said before. You need to take into account how people will play.
The problem with the shield specials is they are defensive moves (most of them). Part of the reason for moves like reflector and nyrul's love is that they offer an advantage for that character. If every character has a shield special, it dilutes that. It also doesn't sould like what is being offered is that fun.Shield Specials, anyone?
Samus's Shield Special could be turning into the Morph Ball and dropping a Super Bomb. Unlike her normal Bombs, the Super Bomb takes a few seconds before finally exploding like the Smart Bomb item. I think this might change Samus's tactics. She might want to lure or throw her opponent towards the Super Bomb so they would get caught in the large explosion and suffer a high amount of damage.
How about Thunder Wave for Pikachu's Shield Special? It is an electric-type move that causes paralysis. Maybe Pikachu could surround itself in an electric force field and it gets bigger to a certain size the longer you hold down the B button. Anyone who gets inside the electric force field would get stunned (but no damage) as if their shields just broke. This gives Pikachu the opportunity to close in and deliver a finishing move (either down+B or smash side+A, you know?)
How about Leech Seed for Ivysaur? It would shoot a seed at an opponent and then the opponet's percentage steadily goes up while Ivysaur's percentage steadily goes down for five seconds. That, or Grass Knot, where grass grows around Ivysaur and opponents will always trip every time they walk on grass. That would give Ivysaur a chance to use Bullet Seed to inflict lots of damage or smash them off the stage.
Most fighting games (unless you are Dante from MvC 3) have anywhere from 2 to 5 moves. Each characters in Smash Brothers has 4. I think they have enough moves.
EDIT: Most of these moves would be examples of potential down specials.