While it doesn't fit with the polymath theme, what about requiring interaction with other guild members to gain their strengths? For example, I kill an arch-mage and cut the brain from the corpse. When I eat it, I temporarily gain arch-mage abilities (or perhaps the capacity to train a subset of abilities). The limiting factors would be:

- Duration
- Capped skill/spell level
- Guild stacking limit

I know the pros/cons with this sort of setup would be much different, but at a glance it seems interesting.