yeah, I think that's precisely what they'll go for, similar to the battlemaster abilities.
You choose in advance if you use it or not, but as you said the resource/spell slot is consumed only if the hit registers.
Of course, this won't allow the granularity of "deciding to use it only if it's a crit", but honestly it would be a reasonable compromise and not something I'd twist my pants about.
I'd be perfectly fine with losing the "smite only if crit" ability. Tbh this ability always felt too gamey to me.
However, theoretical smite hotbar icon will prevent using other abilities at the same time. If Larian really doesn't want to make it a pop-up, then smite (& other similar abilities like sneak attack) should be a toggle instead of an icon. This would also allow smiting on opportunity attacks.
