I think that would be entirely broken. Work a sage, but take an engineer instead for a Mastery building... Not a good idea at all IMO. We are thinking of having settled specialists provide GPP, so there is that at least.
I would like it if the unused GPP were held over as phantom points to counted to the probabilities for the next GP. This would make it much easier to get small numbers of key GP types, while making it harder to generate masses of a single type.
I think having settled specialists provide GPP should be Civic specific. Settled GPriests giving priest points in theocracy would make sense to me.