I guess I'm wondering how they are going to break even in 2015, when their investment is nearly 7x Mojang's highest revenue. I'd guess that a majority of the people on all the current platforms who are interested in Minecraft have already purchased it. I suppose Microsoft could give it more exposure to pick up the stragglers... but 7x?
If they change the pricing model, I think they will face revolt from the community. A Minecraft 2 or annual subscription just isn't going to fly. If Microsoft expects any success, they need to keep things the same, not make drastic changes to Minecraft. It's success is largely in part to it's business model, indi nature, and slow stable growth in features contrasted with low system requirements.
The only place I see for big growth in revenue is in Minecraft servers (ie: Realms). If Microsoft does that really well, there is an opportunity there. But, they are already competing with some stiff competition in that market.
What actually would make most sense is if the purchase isn't intended to break even financially, but were intended to bring goodwill to Microsoft, especially with the younger generation. If they do really well for Minecraft, they might be seen more in those terms than as a hated has-been megacorp. That might be worth $2.5B. Otherwise, I'm just not seeing it unless I assume Microsoft has some failed strategy in mind.