Yep we definitely need to enact legislation that ensures that more than just iOS and Android are available on mobile phones.
How do you imagine that to happen? There are essentially 2 desktop operating systems (Windows, Mac), and 2 server operating systems (Unix, Windows) and 2 mobile operating systems (Android, iOS). Windows failed on mobile despite being backed by one of the most valuable companies in the world. Nokia and Blackberry OSes died even though they were dominant in this space when iOS and Android were in their infancy-- now they can't even maintain a foothold.
What legislation, other than calling for a national institute of mobile OS development, can ensure happens what the market clearly does not want to happen?
There is a reason there is always 2. The market wants convergence because that simplifies everything. Developers want fewer platforms to target, users want fewer tools to learn and versions to buy and reliable integration among the tools they use.
If the market could, it would drive it all to one platform and ecosystem but I think what we see is that there is a fundamental tension between openness and polish. If a system is open, you can't expect it's pieces to work together as well, be carefully reviewed and vetted, follow common conventions etc. If you want a system that works smoothly within itself you limit your freedom of choice. I think that tradeoff is insurmountable-- people here will surely tell me tales of unicorns and leprechauns, but I see no way to maximize both openness and polish.
Windows was a strange beast because it was a closed OS and an open application landscape. It holds its legacy position in desktop software but the future looks like enterprise and mobile systems that are more fully open (Linux/Android) or more tightly closed (Mac/iOS).
I do not see a way to motivate a third player unless the existing solutions fail in their missions. If iOS becomes so unpolished that another closed system succeeds in surplanting it, or Android becomes so closed that another Linux variant gets ported and gains share.