I have a user on another forum who's thinking about buying the game,
But, it's a key thing to consider if customers who buy the Java version after the Win10 version was made available would still be free/redeemable, as the wording on the blog posts appear to be too vague to tell.
I'm sure that there are other customers who would also like to be informed about this current situation too, and I can't find any information about it.
I would concur that assuming is a bad idea, but I can report that I recently (1 week ago) purchased the Java version in hopes of getting the Windows 10 Beta free, and it worked for me. Now running both and able to play with my son (Pocket Edition) on his iPad from my Windows 10 PC and the classic game as well.