Does not look like a good proposition for desktop app developers
ActiveX is back, this time restricted to the MS App store In the hopes of avoiding the security problems that orignally plagued the idea, I suppose.
However, this is not the reason of this becoming yet another dead end for Microsoft. The basic premise seems to be that only the display and input capabilities matter from one hardware platform to another, but this ignores the overhelming differences in CPU power, storage capacity and RAM size of the different devices. MS likely hopes that using cloud services can hide some of these differences.
The idea of having the UI miraculously adapt from one environment to another, which is no small technical feat, is going to work for apps going from phone to tablet to desktop, but it won't work at all the other way around because cloud services can't provide additional local CPU power, or fast local storage, or the ability to work with huge data sets off line.
Still, the idea could bring a number of phone & tablet apps to the desktop, which could at least make the current app store portfolio look a bit better.