Parallel processing would be awesome, but like @BigRoy says, it's slightly problematic. In most cases, unfortunately.
It boils down to that Maya and most other hosts run sequentially which means it can't do two things at once. It can be worked around, and that's the plan.
In a nutshell, rather than running multiple plug-ins in a host, such as Maya, run one host per plug-in.
The remaining issue there is when plug-ins are ordered to run one after the other. Only plug-ins with the same order can ever run in parallel, as there's a chance a plug-in of a higher order to somehow depend on the results of the one before it.
That's simply the nature of ordering and there's not much to do about it technically. It comes down to you ordering with caution and taking into account those plug-ins that are meant to run in parallel.
Any experimentation on this front is more than welcome, the sooner we get a solid workflow for it up and running, the faster I or anyone can see it implemented in the core.