What I want to know is why Mojang/Microsoft bothered to make a completely new branch of Minecraft for just one of a long string of windows versions. Although Microsoft probably did this for win10 promo, how will this affect modding, and vanilla?

Except it's not a 'completely new branch'

Windows 10 version is the iOS/Mobile version.

They brought it to windows for many reasons not the least of which is it allows them to make better use of hardware.

Modding wise, probably won't see anything to do with it for ages.

How it'll effect the java versions, nobody cares.

Actually I do care cause with new versions on the same platform with generate different modding ways... I have tried this win 10 ver. and don't care for it as I cannot edit the specific "keyboard" buttons. Also, no F3

Microsoft has a long history of trying to use games to coax people into upgrading to their next and newest big, slow, buggy, and unpopular operating systems.

 

Back when Vista was the hot new thing, Halo 2 was the big game at the time. Halo 2 was ONLY available on Windows Vista and it was claimed it would not run on Windows XP because reasons..

 

http://www.tomshardware.com/forum/95000-13-halo-only-windows-vista

 

If Microsoft is smart they will be optimizing mc/win10 to run on azure and pricing people into cheaper realms. This will crush the existing market, but only if they can capture the modding scene.

 

To do that they'll need to pursue a forge or bukkit style API. This could also get people using C# which would be a strategic win.