There are a lot of ports from other platforms on http://os4depot.net/
. But in order to make it somewhere we'll need to prove somehow that Amiga is in some way different from everybody else. I think the Natami's exercise on seeing if the Sonnet card will work in their Classic Amiga clone with PCI slots when it comes out is a good idea. If the Sonnet card would work on a PC you might very well have a reverse-bridgeboard-like capability.
The problems arise when you need them to have NVidia graphics card support and different chipset support on the PC motherboard and so on. Also all of the old OS4 software won't work on x86 without porting. That's why AmigaDE was supposed to be so necessary in the first place.