Not so sure I'd want ZX to be an X-series clone. Perhaps copying the other Biometal data instead of having to rip the Biometals themselves off their respective chosen ones and lose them every game, while expanding each Model's attacks somewhat, would be sufficient.
I'm not quite sure about Z. You'd expect the legendary heroes to be strong, but X and Z were frowned upon by Prometheus. Similar to the versatility of X and A, Z and by extension ZX might have a lot of untapped potential because of Zero's learning ability.
Well, ZX gets an extra skill in Advent, which varies by the Chosen One, so it is very well possible. In fact I kind of expect it should we see any sequels. Model ZX, in its initial appearance, doesn't even match up to a buster/saber Z1 Zero, due to lacking the dash-roll. The only thing that really gives it an edge is the souped up aerial roll and the saber's ability to break the buster's damage barrier. In terms of versatility Model ZX is actually pretty crappy.