The pros are are happier developer community.
Apple is many things but it's not a developer tools company - I doubt it even covers costs on the developer programme if you include XCode development and so on. It produces those so people can write software to allow it to sell it's other products.
The only way this move weakens it is if, as a result, the quality of apps declines. I'm guessing that they'll look to head that off by pushing non-XCode apps that little bit harder, at least in the short term, to ensure that they're up to spec.