It already is, by fans. I may be wrong but I think there are actually 2 remakes in progress. Both significant improvements over the original.
The latter is better IMO. It feels a lot more like Adventure and changes some things to make it more fun to play. Silver, for example, doesn't drop held items when levitating in the second (the first doesn't have Silver yet). Tails has a a spin attack unique to this one. Mach speed sections are actually controllable (and pretty fun). There's not a ton of hang time between homing attacks. The spindash is instantaneous. Sonic actually feels FAST and natural to control, as opposed to the twitchy mess of the original. In wave ocean, you can find the purple crystal item that lets you shrink and multi jump (I think it's just a double jump in this one) giving greater purpose to the larger worlds. There's a lot of little visual touches like effects and more effective, dramatic camera work to make it feel more like the game 06 actually wanted to be. Give the dev(s) time and I think this could be a game to compete with Sonic Adventure. I don't think it'll be a match but it'll be one of those things where someone says it is and I can say "I disagree but yeah, I see where you're coming from".