Updating "Add-on" civs to fit 2.9 isn't as hard as making new ones. If no one else updates these civs, I may end up doing it in a couple of weeks. I'd like to add them to "Clash." However, I'm also trying to update the RebelTypes.py file so that revolutions occur correctly, so I'd like to lock existing civs.
Honestly though, there should just be some sort of 'region' and 'colony' tag for civs so that the rebeltypes and culture-linked starts features always work--and players can choose how many civs they want to load based on computer performance.
As for requests, I'd say the Maori, MesoAmericans, Celt-related and Greek-related civs have the highest priority for inclusion. Most other regions of the world are well represented for early age stuff.