I think the big issue here is that WinRT provides less attraction for business, than Silverlight, so I cannot see significant adoption of WinRT until windows 9 or 10, unless Windows ships RT updates between versions, which is an impossibility going by past form.

Going by the past form Microsoft, I am going to be very cautious, it is only a few years until iOS and Android become full blown operating systems. Microsoft are quite a risky company to develop for for the first time in their history.

I am looking to develop a Win phone 7 application soon, but the underlying tech is (allegedly) losing support, that makes Win phone 7 insane to choose as a development platform, if this turns out to be true, Microsoft have effectively killed Windows Phone, I won't touch it with a bargepole.