Here is one think I would like to work on:
better protocol documentation (how we actually implement things!) and integration testing between many implementation.
There is enough bad blood between Fediverse participants already.
If the new implementation is coming I feel like we need to have Mastodon Inter-Client Conventions documented asap.
(Those who remember #X11 may recall #ICCCM - Inter-Client Communication Conventions Manual this is what I think we need)