Anyone who thinks this is going to be on the 360 must be loopy.
Forza shifts consoles, it's a huge deal for MS and with the Forza release schedule tying up to land at anticipated launch of the 360 replacement they'd be mental not to have it as a launch title to get their boxes under TV's. Sony have dropped the ball since the PS2 imo, they should have focused their efforts on getting GT's failings sorted and aimed GT6 for PS4 launch, instead it's coming on the PS3, will no doubt be a spit and polish update of GT5 suffering a lot of the same issues and we'll see GT6 in about 5 years time, by which point even the most blinkered PS/GT fanboys will be losing patience.
As for Forza 5 I'm hoping for more tracks, better lighting and textures, some of the older/poor car models improved massively, active day/night cycles, weather, further improved physics, better damage modelling, open wheelers (be it formula ford type cars, atom/caterham etc or all of the above) some more gameplay options such as having quali sessions, open pitlane online trackday type events. Better choice of wheels/offsets/fitment, bodykits, better paint/livery editor and more cult/retro cars that have missed the franchise so far like the original mini etc. Plus no doubt a bunch of other things I've not thought to mention.
Forza is far from perfect but it's considerably better than GT if the last two offerings are anything to go by. I just hope they keep the NFS physics and gameplay for Horizon and keep Motorsport as a more sim experience.