I think having a distinct separation between back-ends and swappable front-ends would be a good thing, but by this point, it would require government intervention to make it happen. Twitter, Facebook, etc. froze out third-party clients to protect their advertising revenue. They're not going to let third-party clients back in unless they're forced to, and such a move by the government would be tantamount to declaring war on the advertising industry, so, it's not likely to happen.