I get the feeling if TR get anymore Z Crystals it will likely either be Fightium Z (Wobbuffet, Bewear?) or Normalium Z (Meowth).
Darkium Z looks like it could suspiciously qualify for most of TR's other roster should they expand since loads of Pokemon learn Dark moves (even Meowth could potentially use it), while Mimikium Z works to showcase the signature Z Move for the Pokemon (though I admit I'm surprised Mimi-tan didn't end up showcasing it).
I think it really depends if they're planning to keep giving TR focus this series, or they just boosted them for a brief moment in the limelight to check off a couple Z Moves. If they plan on keeping them a ongoing threat they'll likely get more resources to keep up with Ash, but if the writers intend them to go back into incompetents, they'll likely not give them much else and let the twerps overtake them like usual.
Concerning Lillie, I'm tempted to think even if she doesn't get Sandshrew, she might get something like a new move for Snowy, especially since development tends to come in sporadic but heavy bursts this series (eg. TR getting a Dark move, a Z Ring and Mimikium Z in one episode, same for Kiawe getting a new move and his secondary, or two episodes for Lana to get a new move, a Z Ring and Waterium Z).