Does Minecraft Windows 10 Edition accept the New Gamertag System?

do you have a idea of when and if they will ever support it?

No. Minecraft has not been updated to work with the new system.

I bought the Java Edition and migrated it to the Windows 10 Edition, does this not give me a free version of Windows 10 Edition Minecraft, I have to re-buy it?

Having an up-to-date version of Windows 10 does not guarantee that this game actually works on this computer. The system specifications must match at least the minimum requirements.

The Minecraft Dungeons Launcher is not the same version as the windows 10 microsoft store edition, that's why you're being sent to the minecraft website to buy it, since you don't own this version. If you go to https://www.minecraft.net/store/minecraft-dungeons-windows,
you'll notice that there are three options to buy;

• Windows 7 and up: This is the Launcher Edition,
  which you probably do not own.
• Windows 10: This is the Microsoft Store Edition,
  which you probably own.
• Hero Edition - Windows 10: Also the version from the Microsoft store, but the premium edition.

Also note that the microsoft store also shows two versions of Minecraft Dungeons, additionally to the other versions that can be purchased on the minecraft website;

• Windows 10 Edition
• Xbox One Edition

Make sure to have selected the correct edition of it, which is here: https://www.microsoft.com/p/minecraft-dungeons/9P8MK4NC0LJB

Hi Kathy,

Thanks for reaching out to us in the forums with this question. When it comes to Minecraft for the PC, the Windows 10 operating system would be required and it must be version 1511 or later, so Windows 7 would not be compatible as an operating system for
the game. The Java version is available to be played parallel to the Windows 10 version; however, it (the Java version) does not allow for crossplay between players on different platforms. Insofar as different packs for the Java version, it would be best to
check on the Minecraft website if that is an available feature, or via the in-game store.

Minecraft: Windows 10 Edition FAQ

https://www.minecraft.net/

I hope that this information helps out!