When it comes to our beloved 3D platforming mascots, most of them undergo model changes over the course of their history just to keep things a little bit fresh and exciting between mainline releases. Mario is a great example of that, as everyone's favorite Italian plumber rarely sticks with the same model between releases, with Nintendo even going so far as to tweak Mario's model in 2D series after fans got sick of the "New" Super Mario Bros. art style.
It's a little different for Sonic the Hedgehog, that has stuck with the same character model for the blue blur since the late 2000's. Sonic Team usually does something extremely minor to Sonic's model between releases, such as shortening his quills, with only Sonic Boom for the Wii U back in 2014 as the only time the developer has attempted something a little more drastic. I don't think I have to remind anyone of what an absolute disaster that game was.
Having had roughly the same model for so long, some Sonic fans out there think it's time for a bit of a change. The topic was recently debated in the Sonic the Hedgehog subreddit, as hundreds of fans put forward their opinions on whether the blue blur should stay the way he is, or if Sonic Team should put a bit more effort into a new model for Sonic for the next mainline game.
The more popular answer appears to be that Sonic could do with a few tweaks here and there, especially when it comes to his facial animations. A lot of fans seem to think Sonic is a little too rigid in his face which stops him expressing more subtle emotions, something which probably would've helped a little bit in Sonic Frontiers.
Not everyone shares that opinion though, including u/FelisMoon who thinks Sonic needs a complete proportional redesign. They stress that Sonic's clothes and visual characteristics shouldn't change, but the proportions of his hands, feet, quills, and everything else should so he doesn't look awkward when he's just stood around and his hands don't clip through and block certain parts of his body.
Finally, there are those such as u/kjm6351 who don't think Sonic Team should do anything and that Sonic's fine the ways he is. Rather than have to put up with potential complaints, they say that Sonic's model feels like a "if it ain’t broke, don’t fix it" kind of situation. Considering how well received Sonic Frontiers was, it's a pretty solid argument, though it seems the general consensus is that Sonic is due a tweak or two. We'll have to wait for the next mainline Sonic game to see whether Sonic Team listens.