Consider splitting fallback directory list into two: stable relays and very recent relays?
This is based on a conversation with @arma on IRC.
Fallback directories is currently selected from a rotated set of Tor relay nodes that we consider to be "stable": they have been around for a while and stays available for a long time.
For anti-censorship, it could make sense to also bundle a set of relays that is very recent in case there is new relays which the censor haven't blocked for yet because they haven't updated their list of known relays in their blocking system