Better search functionality
The current state of postActiv's search system is pretty sad. It's very slow and it doesn't contain options for faceted search.
We could have plugins that implement an external backend like Solr or Sphinx, but I also think there could be something done with the core search functionality as well.
(Relevant discussion: https://gs.archae.me/notice/264469)
Desirable but not really a huge priority until the bitrot is dealt with.
For the record, the Sphinx search is what was historically used on Identi.ca prior to the pumpio split.