This is a solid idea, but I don't think it works well with every background. What would you do with the Outsider? And some can be split up into multiple ones. The Solider Background covers everything from the warriors to the non-combatants to the generals for example.

I think that requiring both a feat and an attunment at the same time is a steep price to pay for something, unless that thing is very good. I don't know the system enough to say if it's balanced.

I would use something like this, it would give some helpful structure to what the NPCs can do.