I prefer mechanics which reward thematically appropriate interactions over those which punish inappropriate ones. As such I'd love to see an option where a class doesn't receive its hp bonus while wearing non-proficient armor, instead of simply being disallowed.

Failing that, an "encumbrance penalty" applying slow, mining fatigue, and/or increased cooldowns could be an interesting alternative.

we like this idea and are going to look into it, no firm eta but it should be doable