If I were a betting man, I would be that Kenshi, Sonya, Johnny Cage, and Jax will all be story participants but will not be on the active rosters in game.
These decedents have similar abilities to their predecessors and including all of them would be redundant and wasteful.
Takeda has a similar skill set to Kenshi, Cassie is a amalgamation of of Sonya and Cage, and Jacqui is super boring, just like Jax.
If you read Boon's original comment:
He is pretty deliberate in saying "Story Wise" in his comment. Obviously just my Opinion. But I think it is a bit of a necessity of they are going for a cleaner slate.