People may disagree but you need to hear this: Shadow Generations is essentially Frontiers 2.

ShadGen inherited many similarities from Frontiers in terms of:
1. Its "open zone" world that gradually opens up more and more,
2. Unlocking more and more abilities as you progress, just without a literal tech-tree,
3. The whole Cyberspace shit where you get warped to a stage from the past and play through it (granted this was already in SonicGen).
etc. etc.
Some Sonic fans are asking for Frontiers 2 without understanding that we've already gotten Frontiers 2; it's called Shadow Generations.