My bet is on Brian Tyler. Rambo, Expendables, he's got the current track record with Stallone. I imagine Tyler will try to incorporate some of Conti's style into the score, but my expectations for this film and score will probably not be very high...
Nobody knows the ROCKY sound better than Conti. Why get someone to incorporate Conti's style when you can get Conti himself?
The film has a director now. A newbie named Ryan Coogler, according to IMDb.
Hopefully he will hire Conti. If they're going to monoploize on a character, the son of a one-time character, and the franchise rather than stand out their own feet with new characters unrelated to the Rocky universe, then stay the course and hire the composer who helped make it was it is.