I think it really depends on how much control Apple intends to exercise over the IP. Could someone fork it and use it to create a mobile platform that would be free from legal harassment if it competed with the iPhone?
Why not bridge the "yet another cross-mobile-platform development framework(s)" that were written for Objective-C, the same way Apple did with their frameworks? There is no need to restart them all over again in Swift to access them in Swift.
Perhaps you were attempting to suggest that no quality cross-platform frameworks ever materialized for cross-platform development under Objective-C? (there were certainly attempts, including from big players) But if that is the case, I'm not sure an arguably better, but not dramatically different, language is going to change anything.