So I just write something long about this and it failed to send. Now I'm going to shorten it.
My question about all of this is how about Steam? Origin? Uplay? Would you still need to register to Uplay on PC when I buy a Ubi game from MS? Or MS store can function as a dumb store? Or Ubi simply wouldn't sell on it? Or we can buy different versions on PC (MS, Steam) making the PC more fragmented.
Personally, I like Steam the most because it is the cheapest. I'm not talking about discount but more about the different currency rate that Steam apply. FYI, almost all big online app store apply their on rate vs straight currency conversion, but Steam is the most generous out of all the stores. New games at $50-60 games can be bought at $30-40, and yes, that is the initial price. I don't think MS is that generous (current MS app store is better than Google play in terms of rate, but not at the level of Steam).
Maybe this should be splitted into its own discussion.