Well there is a rumor going around Sonic Adventure might get one. So who knows. If it does not happen by the time of the next mainline Sonic game reveal... then I'll say it likely won't be happening at that point.
I still don't get why everyone wants a Sonic Adventure remake. The game is fine as is and if on the unlikely circumstance that Modern Day Sonic Team don't completely screw it up, I just know it would lose all of the charm the original had. I'd much prefer a good new game than a retread.