This is going to get interesting
As a long time minecraft player, knocking on for a decade, I am concerned that Microsoft will turn the account in to a pay-monthly affair, which will turn me off completely.
As far as I'm concerned, running my own server, the costs to Microsoft are down to onward development and bug fixing of the game itself... which is not an insignificant cost, but Microsoft could certainly freeze development for those of us on the Java version, and only provide authentication services.... and lets face it, there will likely be an authentication service which will run locally and only require a host file redirection... it's been done before for other games, and I have little doubt it will be done again.
I'm certainly not signing up to a subscription service, that's for sure. I think Microsoft might end up shooting themselves in the foot if they do it this way. I dare say it would be a major publicity disaster for them.
I do believe that Notch should have kept his promise to give the game to the community when he was fed up with it. I hope his money is keeping him warm at night. It doesn't seem to have done anything to spur his efforts in other ventures as far as I can see.