Im familiar with the vsti version of openmpt, and also the awesome and free alchemy player. I should note that after i posted this i fired up openmpt and was completely amazed at how quick the workflow is for me compared to other hosts.
My main issue is that i really like the sampler and the mapping stuff in openmpt. When i'm faced with layering, i do use other stuff, but if it was itself a vsti, i could use it as part of a layer.
Probably to insane a project to expect someone else to do...
One of my thoughts was that maybe as a fork, it would get extra focus that could be ported back to the main program. As a sampler, those features that need to be repaired or enhanced would stand out more without the shadow of the main program.