I really hope that one of these empty slots is a Union Cross remake because that game's story is too good to stick to mobile.
That's my guesstimation, too. Spiritual successor games to 358/2 Days and Birth by Sleep.
In the 5 min soundtrack trailer shortly before the end there is a part labelled "Second memory" while showing off Axel/Lea and Sora both together with Roxas, so maybe that's one of the two incorporating the "twilight gang"-side of things while the last one is something with TAV.
That's my guesstimation, too. Spiritual successor games to 358/2 Days and Birth by Sleep.