It's not just driver development that's the issue. The Amiga PCI busboards don't behave like PC PCI busboards (unlike many non-PC solutions which do--e.g. the AmigaOne). In same cases, the busboards don't provide the resources needed to bootstrap the device (e.g. SCSI HBAs and generic VGA adapters). So, any new implementation of a peripheral bus would have to be very PC-like for it to work with off the shelf hardware.
It's possible to work around the issues I mentioned above, but it limits the amount of generic programming one can do.
Trev