The NT Kernel can be recompiled for any process with a bit of glue logic. The reason microsoft wanted to drop teh other platforms is that they don't want to do driver support.

The reason the Alpha is still around is that it uses a PCI bus and PCI adapters as opposed to a proprietary bus.

CE is the NT kernel without most of the drivers required for a PC: multiple bus drivers, multiple file systems, midi devices, storage devices ... (Yes it can run on a strongarm).