Mixture of Experts is already used by pretty much all modern LLMs to address exactly this phenomenon.
Hopefully, future models can be trained to be even more aware of external knowledge, accessible through web search / RAG / whatever it will be then, and might not need to internalize much knowledge at all.
I suppose the right approach would be to run queries like the ones you want your model to be able to do, sort weights/experts by usage frequency and then reareange the weight so that all but the most frequently used can stay on disk. Tricky though, it could be that a e.g. database question uses 90% of the network at some point or another
Edit: I guess at the moment this is just having an LRU cache of experts
Hopefully, future models can be trained to be even more aware of external knowledge, accessible through web search / RAG / whatever it will be then, and might not need to internalize much knowledge at all.