I don't think that's correct either. My understanding is that the issue with DirectX 12 is that it is limited to Windows 10 - So people still on Windows 7/8 can't play DX12 games. AFAIK, you can use DX12 in non-UWP applications.
Microsoft could do a million things, but speculation doesn't get you very far. In general, it's better to have some actual facts to go on.
One of the actual facts in this case is that Microsoft makes the vast majority of its income from Win32 programs, including Office 2016, not UWP apps.
Another actual fact is that Apple, Adobe, Google, IBM, Oracle and other large software companies also make their money from Win32 programs, not UWP apps.
Another actual fact is that all these leading companies are quite happy to launch lawsuits and/or to approach the US DoJ with accusations that Microsoft has done something anti-competitive.
All of this means that Microsoft cannot possibly close off access to the Win32 API, and even limiting DirectX could be a big risk.
It also seems to me that the PC games industry could quite easily be delusional about its significance in today's software industry, and that it's not aware of the full picture ;-)
