So, Neil & CJ, when you guys were writing memory palace of the sage (the creo mentem ritual that lets you put an entire book into your memory palace) you hadn't seen the rules for casting tablets yet.
The interaction between these two rule sets doesn't seem to be that bad. The ritual really does take 5 pawns of vis and castng a spell from a casting tablet isn't quite as nice as learning the formulaic.
But let me put this out there for people to chew over and see if this could be exploited more than I see.
A character needs to have the skill magical memory.
Once they have this skill they can learn a level 25 ritual to memorize books
I imagine that casting tablets could be subject to this spell
The number of things that can be stored in a memory palace is limited, so the prospect of someone witha personal vis source in mentem pileing up absurd quantities of spells in their mental library is not an issue.