Sorry it took me so long to reply.
We have a modular application that can dynamically load components (it's a Prism application that uses Navigation callbacks to load modules on-demand so we have shorter startup times). Rather than have one giant model assembly for everything, each module has its own domain model, and this model is registered during the module initialization process (we just add it to the list of probe assemblies). Ideally, we'd like to have it "just work" (i.e., adding a model to probeAssemblies causes the internal list to refresh), but failing that we were hoping for a way to force that refresh.
Right now, we've created a workaround where we separated the modules into a "domain model" module and a "functional" module and placed the domain model modules dependencies in the intial module catalog of the Prism app which therefore force-loads all of the domain model assemblies at startup. However, this causes startup overhead (larger XAP file, etc.) we'd like to avoid.