Actually Maxwell can reuse optimisations across users by clever caching. (A cool side effect is that the more it is used, the faster it becomes for everyone).
How do you anonymize and segment the cache to make this not leak PII? This seems prone to analysis showing that users who tend to take left branches in the user lookup trie (low alphabetic user names) also tend to render trees more than desert (so re-order the switch targets to optimize cache), suggesting that “Aaron” might live in Appalachia, not Arizona.