Well, that was quick: Despite Microsoft saying that Windows 10 was coming to its misfit tablet, the Surface RT, that isn't quite the case. As Thurrott reports, Redmond is working on an update for Surface which will have "some of the functionality" of Windows 10. The SuperSite for Windows founder goes on to say:
"Since those [Windows RT and Surface RT/2] are the only Windows RT devices that ever sold in any measurable quantity, two conclusions are obvious. Other Windows RT devices may not be updated at all (i.e. this Windows 10 subset update may literally only be for Surface RT/2 devices). And more generally, Windows RT is dead."