JackOfAllTirades
Explorer
My own personal house rule:
When attacking with your pact blade, you use Charisma instead of the usual ability score.
It's worth noting that Druids require a cantrip (Shillelagh) to gain an ability equivalent to this. And TomeLocks can borrow this ability, but it still requires taking the Druid cantrip.
I think it's a great idea for BladeLocks, and it won't break the game, but (IMHO) it probably should require either a cantrip or an invocation.