As a result of discussion in EZP-25916 an idea popped up to create a task to try to improve User Cache Generation performance. The idea is based on joao.inacio@ez.no work done in PR https://github.com/ezsystems/ezpublish-legacy-ee/pull/100
There's quite a few things in eZUser class that can be slightly (having in mind we're on stable branch) optimized hoping for a better performance.