it'd be cool to see tails be able to use his tails in completely different ways, like by using them to hover, attack enemies by spinning them in a fan, or charge up a powerful dash.
It would be interesting to see them take some inspiration from the Adventure series for Tails. Perhaps replace his spin state on the ground with his tail spin attack, which can't gain much speed but doesn't really lose speed either, and gives more freedom of movement, making it a fair tradeoff to Sonic's spin attack. This would mean taking away his ability to spindash, but that could present an opportunity to replace it with the peelout, which would make him even more different from Sonic in that charging while standing still wouldn't be mostly the same thing as spinning while running anymore.
I'd probably also tweak his flying a bit so that it works like a hover when you just tap into it once, and you hold either jump or spin to raise/lower yourself. It would still make him tired after a while, but perhaps raising up tires him out faster than just hovering? This would also work as a fair tradeoff for Metal's hover also likely being replaced.
knuckles on the other hand, could be way more of an exploration focused character than he already is. give him a way to use those powerful fists of his by vaulting off of enemies or pinning himself onto the ground to charge up a more powerful spindash or peelout. alternatively, he could pin himself in a wall and achieve true 360 degree aiming and launch a spindash while up there.
I've heard the idea of Knuckles being able to charge a peelout to run up a wall before, IIRC he might have even had a similar ability in Sonic Advance 3, but it's been a while so I might just be remembering wrong. I quite like the idea of this being implemented into SRB2. Maybe let him aim it 360 degrees and use it to travel across walls faster, but at the cost of free movement while using it, stuck in the direction he aims it? Perhaps it could even be used to achieve extra height and/or distance off corners/cliffs?
In regards to Sonic himself, while I am a thok fan, the decision has clearly been made to replace it (and probably give it to Metal, though I hope they at least give Metal a bit more to make him more unique than just being old Sonic) and as such there is an opportunity present here to give him something totally new. I've tossed around a few ideas regarding this before, but I'd rather not turn this into yet another "Sonic's double jump ability" discussion thread, so I'll opt to just discuss a few other options for Sonic's moveset instead.
One thing I think would compliment Sonic quite well would be giving him the unique ability to press spin in the air after using a spring or running off a cliff or etc. to curl up. This would prime him for use of whatever his double jump ability is, giving his gameplay more flow and a sense of control unique to him. Alternatively, he could just use it to land on a monitor or enemy to bounce off instead of taking damage.
Additionally, I'd like to see Sonic gain a buff based on how quickly he's spinning along the ground. If he gets going fast enough, he would be able to beat enemies that usually take two hits by hitting them just once and avoid getting knocked backwards by shields. He also rolls across the water at these speeds instead of skipping. This would reward him for reaching fast speeds, as well as make it a bit easier to keep those speeds going. I wouldn't give this buff the ability to break spikes, as this would take away a bit from Metal's uniqueness, though perhaps this trait could exist while Sonic is super.
Speaking of Super Sonic, I feel like it's about time he got a moveset revamp as well. Obviously with the thok being replaced, there's an opportunity to make the Super Sonic version of his double jump ability super charged in some fashion. I'd also like to see his hover ability made native to running off cliffs/edges, with him still falling if he slows down too much, but with him being able to simply jump out of the hover gaining a little height in the process as well. This would remove the need to hold spin to perform the technique, and add a little bit more practicality to it since you would be able to jump out of it rather than jumping into it. This version of the hover could also be extended to certain other "super forms", such as Metal and maybe even Fang if he gets his bike.
