Id like them back. But with some changes.
First we get a second item slot, this one is exclusively for ZCrystals. That way we can still use other items. Additionally, lets go ahead and throw random lore in there that the energy from M.Evolution, and the "light" from ZMoves are not compatible, meaning you can ZMove and M.Evolve on the same Pokemon.
Second change Id make is giving every ZMove type a second attack form. The gen7 ones would stick around and be used for Pokemon not gaining stab. But a new more crazy looking (maybe more powerful?) Move would be used when your Pokemon has stab.
3rd Pokemon exclusive ZCrystals are gone, instead the correct typed ZCrystal used with the correct move, on the correct Pokemon causes the unique ZMove. For instance. On Snorlax NormiumZ and most Normal Attackd Cause Breakneck Blitz, but when used with Giga Impact we get Polvarising Pancake.
4th, and this is simple. In options menu, option to turn of Zmove dance, Zmove annimation, or both.