I am not sure what/where the discussion on the future of ProjectPier and if this has even been a focus as of yet, but I think that an API or the like should be the first thing developed for ProjectPier.
If an API doesn't seem feasible then maybe a Hook and Anchor design pattern should be implemented (similar to vBulletin's hook manager). Then again the package manager system found in SMF [here] and other applications would be useful.
Basically I think that in order to allow for ProjectPier to grow and enhancements to take place these should be developed so that we don't have to go line hunting and worry about updates.
On a side note I would like and will be available to help in the production of this if needed.