Past editions/other games have a dedicated skill to Using Magic Devices, which I like. It has the flexibility of being allowed to cast magic from scrolls regardless of your class, but the costs of still having to put points into that skill and a chance of failure, so you don't step on other classes' toes as much. Even nonmagical classes could put points in the skill to use scrolls.
I'd be in favor of something like:
- DC 12 + spell level [Arcana/Religion] check to use an [Arcane/Divine] scroll if the spell isn't on your spell list (or you can't cast spells normally), restricted to those who have proficiency in those skills. A failure results in no effect and loss of the scroll.
Proficiency + a moderate ability score will give a bonus of +3-6ish, so characters will have a >50% chance of casting a cantrip or level 1 spell. Importantly, the chance needs to be low enough that I'd be willing to attempt it, but high enough that it's not practically guaranteed.
