lets hope they make it windows version agnostic, that way we can all start supporting ie12, instead of being shackled to ie9
8 is the latest for XP/Vista
11 is the latest for 7/8/8.1
9 is still popular because not everybody upgrades browsers, but giving users who don't upgrade browsers a new option is unlikely to be helpful.
Communicating to them that IE is going away and that they should upgrade to a modern browser, "Spartan" or otherwise, would possibly help this situation, as the author suggests.