With the announcement of Final Fantasy going multi-platform, I've read some other stories about how MGS4 may go mutli-platform as well. I thought MGS4 was only compatible with PS3 because how Blu-Ray offers more storage and the cutscenes needed to take advantage of that. So how would an Xbox MGS4 work? Would they just cut some cutscenes or just redesign the game entirely?  

2 to 4 Multilayer DVDs

Or you could stop worring about it and play games on multiple systems

Also, the 360 update is going to patch in HDD installs so there u have it

Good day sir

I somehow doubt that it'll come to 360.  Kojima himself said that the game took advantage of all the Cell processor's cores.  It may have been compensating for the BD's slow disc speed, but I think it will stay exclusive.

It's possible it could come to the 360 or PC but ports of MGS games tend to be a bit sloppy. The PC versions of MGS 1 and MGS 2 were a bit temperamental to run and had (and continue to have some glitches) and the Xbox version of MGS 2 had some problems as well from what I've heard.  I think they outsourced the development of  all those ports to other developers which probably contributed to the problems.

I thought Kojima himself didn't want it coming to the 360?

This isn't gonna happen. Plain 'n simple. MGS4 is too much of a system seller, Sony'd sell their collective children to keep hold of it.

With FF13 gone sony needs an exclusive. There not going to lose MGS4.