I didn't read through the entire thread however thought I would point something out (maybe someone else did too).
MS actually doesn't lack exclusive IPs at all. They have PLENTY of them. The problem is they seem VERY bad at handling the majority of them. So of course there are Halo, Alan Wake, Forza, Fable, Gears. These franchises get regular entries (Alan wake maybe not but it seems we got the first, now the arcade game and the second is in development). Then there are some that have been semi-regular this gen but seem to have been put to the sidelines a bit such as Viva Pinata, Ninety Nine Nights.
However let's look at some other exclusive IPs (I'm kinda ignoring handheld games as they are quite a different kettle of fish)
Kameo
Perfect Dark
Banjo and Kazooie
Conker
Crackdown
Lost Odyssey (possibly?)
Blue Dragon (possibly?)
Too Human
Shadowrun
So firstly let's just look at those rare titles! Perfect dark had one entry at the start of this generation that was reasonably well received.... then nothing just left to die out. A popular FPS series ignored..... why?
Banjo and Kazooie? One entry this generation that was experimental. No attempt to make it their own Mario.
Kameo? One entry at the very start of this generation, was well received and sold moderately well (went platinum hits pretty quickly). Could have been MS's own Zeldaesque/platformer franchise. However it has been ignored since launch.
Conker? Completely ignored. They did a remake of Bad fur day for the original xbox then left to die.
Crackdown? Totally mismanaged. Had a poorly hyped up sequel set on a slightly altered map handled by a new studio. Still managed to be a good game but lacked new feeling. Huge potential in this series.
Too human - Needed to be handled better. MS should have stepped in and helped SK a bit with gameplay. Could have been Microsofts hack and slash series.
Shadowrun - How ridiculously mishandled. Rpg series turned into a FPS. Series seems to be dead and no attempt to revive it.
For both Blue Dragon and Lost Odyssey I'm not sure MS owns the rights to the IP. However the games were well received. I'm guessing they didn't sell up to expectations and so were abandoned instead of making a push.
MS has enough franchises it just needs to use them better. Get a new perfect dark, Banjo and Kazooie, Conker, a proper crackdown sequel and a sequel to either LO or BD and bam a great line up. Throw in a viva pinata for good luck.