Do you guys know about Sonic Mania and Sonic CD? These are fan made games. BUT the guy who made them showed it to SEGA and they gave him permission.
Right now SONIC CD is an authentic sonic experience on Mobile.
One of my friend is working on an HD remake of an old game. and he is planning to create a DEMO 1st and then will show it to the company. If company would agree, then he can continue on it.
(I am sorry, as I cannot mention his name and the name of the game he is working upon. I do not want to spoil his 'half-baked cake').