An HTC One M9 for Windows should be happening this year, according to a recent @upleaks leak, which claims that the “Hima”, believed to be the 2015 Android flagship from Taiwan, will have a Windows twin. This would be something similar to what HTC did last year, with the HTC One M8, and the HTC One M8 for Windows.
While the consensus is that the 2015 Android flagship will make an MWC appearance at the March 1 HTC event, the leak claims that the Windows counterpart will not show up in Barcelona. That is also something we can believe, as the One M8 for Windows was announced in August of last year. Additionally, just like the 2014 Windows Phone, the HTC One M9 for Windows (tentative name) will probably be a US-only device, probably like the Verizon exclusive on the One M8 for Windows, which later made it to T-Mobile.
If this turns out to be true (and there are solid chances for it to happen), the HTC One M9 for Windows will likely run the new Windows 10 phone. At the moment, HTC didn’t officially announce anything regarding a possible Windows 10 phone update for the HTC One M8 for Windows.