IMO we should leave the protected properties unchanged as we create more problems than benefits at this stage. I agree that those should be private but the codebase concerning private/protected, underscore/non-underscore is very inconsistent throughout the project anyways at this time. We should fix that in 3.0 as long as you don't have a certain reason why you need protected properties to be changed.
Still removing the underscores in private properties is fine for me :)