Ngl, I like gimmicky evolutions. But I agree with Inkay's evolution being the worst of those "gimmicky" variety.
Honestly, I'd like to see an evolution that requires to be in a Sandstorm/in a desert-like area to evolve the Pokemon. We've never seen a Pokemon that evolves this way. Maybe it'd be a good evolution for a Galarian Helioptile, or a new ground type. There are plenty of animals in the real world who adapt to harsher environments, and desert environments/sandstorms are QUITE a harsh area.
We've had Pokemon evolve in an electromagnetic field (Magneton to Magnezone, and Nosepass to Probopass), and Pokemon that evolve in a colder climate (Crabrawler to Crabominable), but never a sandstorm.
I also want an evolution that plays around with certain status problems, like a Pokemon evolving by leveling up while being poisoned? I could see this evolution type working for a first stage Grass Pokemon that becomes part Poison through this evolution method. I don't know, I think it sounds cool.