What sort of "worksite" would do you propose for the athenaeum to produce arcana tiles? Internally, it's called a worksite, but we just need to decide what sort of characters "work" there, and what sort of "work" animation they employ.
If we have some foreground piles of artifacts, we could have some sort of sage/scholar/arcanist dig through them when the floor isn't busy, occasionally popping out a arcane or loot item. We should pick two categories, so these characters aren't producing too many matches on their own; I think loot is a reasonable fit, but we could maybe do gear, instead. We could probably get more creative with the type of character, though.
We can split up the Coffers and the mimic floor. The Survivor's Surplus sounds like a good option, but it is probably a little too elaborate for now (there's a lot of exposition there that we may want to convey to players). Perhaps if we had more floors that acted as stores for the heroes; I already have a couple of others on my big list (a Tomb of Tyrants historic site gift shop and an infernal lemonade stand), and I was planning to group these in with the eventual "checkpoint" type floors, where the characters will be compelled to linger a while. We'll see; it's definitely an interesting concept =).