Making divine smite a pre-emptive thing that you pre-load would drastically diminish its flexibility and lead to all of the exact same problems that auto-reactions have - you paladin will end up burning their level 5 smite on a 5 hit point goblin zombie minion that provoked an opportunity attack, rather than on the lich they intended to use it on. That should never happen, ever, full stop; it's a massive weakening of the ability.
I'll take anything as long as the game does not pause the action during an attack animation and prompt me every. single. time. I hit something.
They can buff the ability in other ways, grant more uses. There are ways.
An opportunity attack wasting special attacks as an auto-reaction is exactly what they need to fix. Maybe
that needs to prompt if the weapon is charged with something. Even though I generally hate the idea of reaction prompts in a video game.
They need some kind of hybrid system for reactions where they are automated where that makes sense, still offer a prompt where it's absolutely necessary, and some reactions are changed into Bonus Actions or Free Actions where that makes sense.
