Probably, CoD or GTA. But those IPs are so profitable as multiplat games that it wouldn't be financially worthwhile.

Its significantly cheaper to undercut Sony on price and bundle games.

Honestly, the realistic thing for Microsoft to do at this point is to get indie developers to make quality games for their system. They could then acquire these game developers to make first party games for them.

But then again, they just destroyed their image on how they treat their indie developers...
So I am out of realistic ideas at this point.

There is no realistic option right now.
I think MS would be better off developing a killer franchise by themselves, and who knows, maybe secretly they have been doing that and will blow everyone away at E3 2015....but I doubt it.

An existing franchise that could turn it around and propel them to #1 would be way too expensive, guatanteeing unprofitability for XBox forever.

I don't think that there is a franchise that they can buy that will boost their console sales that much. Also, if ms tried to buyout a franchise, it might irk more people than bringing them to the console. Honestly, if they created several NEW IP's that were really good (non-shooters), it would help sway more people into buying a xbone. Plus those can be turned into franchises that are fresh.  

Lack of new iP's that are good and aren't kid games is nintendo's problem and why they're sales are crap in my opinion. Sony tends to have more new IP's every console generation that are rated highly than the others. Personally, I rather have fresh experiences on a consistent basis rather than the same ol' ****.

Instead of spending 2.5 billion on Minecraft, MS could have sold 25 million consoles at an extra $100 loss. A $249 XBox One would give them first place.

The fact MS would have to buy their way into having a chance pretty much sums up their plan...if you can't make a great franchise buy one

Microsoft already has a hole the size of a mountain after buying Minecraft. Sure they still have tons and tons of money, but buying EA would enrage the investors, because of all the money spent and they don't trusting the Xbox brand all that much.

No franchise alone would do that. Besides wiisports which franchise outsold 80M?
If Nintendo top quality IP haven't done it nothing alone will.
I mostly buy 1st party on Sony and there isn't a single 3rd party that alone would sway me since none of ms 1st parties entice me and most 3rd release on ps.

There isn't a single game series which can turn the race around nor will selling the console at a loss. The only way I can see Microsoft can win this is through buying a studio.....someone of the likes of EA or Activision. The others Take 2, UBI, Square Enix etc just don't have the scope. Nintendo would be interesting in that it would bring with it hoards of family gamers but this goes against the way the XBOX markets itself which is at over 18s.

If they do buy one of the large players, expect the other one to jump into bed with Sony though.

Buy CoD and Fifa and Playstation would be in serious trouble.