I figure Insomniac must be most likely. I know they build their own engines vs using middleware engines like U3, but they have made it clear publically they will help other developers with coding on PS3 and with their 3rd PS3 game due soon who else has more experience of delivery games on PS3? Most other developers have 1 release (of this scale) and that was often late.
I'm curious whether they port from what they have or move to more recent U3 engine and port over code/content to a new U3 version. Given that UT3 runs very well on PS3 and received a lot of tweaking it might make sense to switch to a more PS3 friendly version of the core middleware (or it might not make sense for many engine reasons I know nothing about!).
Try to be reasonable... its easier than you think...
