I've been thinking on some changes for counterspell, for dnd and any other rpg that has counterspell.

My thought is moving counterspell from a spell into a game mechanic.

If a creature casts a spell that you also have the ability to cast that day, you can expend an appropriate spell slot to unravel their spell and counter it.

So just about anyone can counterspell but does limit it to creature that have spell slots. It makes casters think more about encounters that might come up that day and also push them to choose more obscure spells that are less likely to be countered.

Any thoughts? Arguments for or against? Other ideas you've tried?