Ribbon Girl's double jump and Ninjara's dodge are already general Smash mechanics.
My money is still on Spring Man default with either a Ribbon Girl echo or a Bowser Jr. / Hero style character swap for Ribbon Girl, Ninjara, and Min Min.
Either way, we're getting more than one character represented in FP6.
Ribbon Girl doesn't have
a double jump, she has
four mid-air jumps
.
Ninjara's dodge has him disappear entirely and reappear.
Neither of these are "general Smash mechanics", at best they are character-specific Smash mechanics, and they are only on characters that
make sense to have them as mechanics. Kirby characters have multiple jumps because they have multiple jumps in their home game, not because they are in Smash Bros. You are suggesting they slap a ninja teleport and meter mechanic on Luigi because you think he is too boring without it. You don't even know about the mechanics you're generalizing, so stop GENERALIZING THEM.
Again, the same reason Byleth uses all three lords weapons,
is because Sakurai thinks there are too many swordfighters, which he has expressed time and time again. He didn't let all of the three lords share the same moveset and use each other's abilities either, he added onto the avatar character.
the reason Young Link uses Fire Arrows,
he has them in actual Zelda games?
the reason Ness and Lucas use Starstorm and others,
An actual case of expanding a character's moveset with things they can't use, but their movesets would otherwise be entirely support and healing based with one PSI attack otherwise.
the reason K. Rool can use all of his different Persona's abilities,
is because they're all him?
the reason Joker uses moves that aren't even originally from Persona,
Like what? Everything he does is either tied to his "phantom thief" aesthetic or something he could actually cast in Persona 5 (Eiha and Eigaon are in Persona 5, Tetrakarn and Makarakarn are also in Persona 5). He isn't stealing the Personas of other characters to flesh out his moveset because he has enough of a moveset already.
You could easily make an Arms conglomerate character 100% more interesting than picking one dud of a character who can kick. It gives Sakurai a lot of opportunity for one of the most interesting characters ever.
I really don't get why people are so against this. It's just speculation and it's just what other people like as an idea for the character. And yet, it apparently ruins the entire character because it isn't just one but many. Seems kind of backwards.
The reason people are "against it" is because the only people who are "FOR IT" are operating under the assumption that an Arms fighter is a "dud of a character" in the first place! An interesting character isn't comprised of stolen mechanics from everyone in a single game. Shulk didn't need Dunban's sword and Melia's magic and Riki's status effects to be a good addition. Banjo and Kazooie didn't use Conker's chainsaw and the Battletoad's anvil fist. Interesting characters are made by taking one idea - "what if we had a fighter who could do this" - and taking it to the logical extreme. You never see this "JUST SLAP THEM ALL TOGETHER" mentality on any other newcomer.
Why can't people just take the L and admit they don't care about ARMS? If we can have an 8th Fire Emblem character who is still portrayed with a sword for all of their official appearances, then a stretchy arm person can surely get in as is.