I think Momento's are cool and add yet another hard to acquire reward due to low RNG. I would think it would be cool if we got more than the three current Momento's, maybe make an Iron Banner Momento for an IB Keepsake shader, or make some Dungeon-specific Momento's with a unique keepsake shader per Dungeon. I am totally fine with what we have, but imagine if we had more types of Momento's and Keepsake Shaders, that would be a cool idea.