Recently Famitsu had an interview with Takashi Iizuka, in the interview  it is revealed that there is a new  entry in development. Though there is no other information it is still something. You can check out the exert below-( Translation from Soahcity)

Famitsu: Finally, our last question – please tell us about Sonic’s future.

Iizuka: We at Sonic Team – are developing a completely new game, as well as developing a full movie, actively done by Sony Pictures, and animation on Sonic Boom. We are also ready to improve sponsor ties.
The most important thing is not the fact the series survived for 25 years, but how many games was developed.
Our goal – add something new and overcome any potential hardships.

Sonic,The fastest thing alive-

Below you can view a video celebrating Sonic the Hedgehog‘s 25th anniversary. Feel free to leave a comment below sharing your good ol Memories from when the franchise was still alive and kicking.

-Gotta go fast-