Will we see them soon? There is so much material around in the lore they could use to make it happen, frankly I’m surprised it hasn’t come a lot sooner.
Regarding night elves and druids of the flame, I think the blood elves should get druids of the flame, the rebel druids of the flame (who rejoin our side) should somehow take their druidic mastery and like the Illidari did, get blood elf nature lovers who have that fire theme, involved with them.
I’d love to see Nightborne as Valewalker balance druids, trained by Farodin and his night elven Valewalker druids, since it’s a balance druid and mage organisation that is responsible for the Arcan’dor.
Finally I’d like to see void elves come in and help the druids with the nightmare, and learn druidism from there their joint efforts save the remaining Darkgrove druids of the nightmare, restoring them to sanity, and this becomes the branch of druidism void elves mainly belong to.
In all of these, they are all tied to night elven druidism rather than Zandalari Troll or Drust Kul’tiran druidism, because druidism is an elven thing, and all the elves inherited love for nature alongside arcane aptitude from the night elves. So if other elves become druids it should be via the main elven root of the discipline, even if they adapt and make versions or niches of their own.
The separation of the exile and isolation of the Night elves during the Long Vigil may have prevented Thalassians druids from developing as a powerful force once they had fully settled in Quel’thalas, but much has changed since WC3 when the night elves came out of isolation, for starters druidism crossed factions into the horde, as well as demon hunting, both came from the Night elves, to blood elves and tauren.
I can totally see newer Nightborne druids encouraging blood elves to take that extra step into full druidism, and off course, void elves would be all over studying the void effects in nature and finding ways to help Azeroth fight against it with their knowledge, this would deepen void elf - night elf ties which should have other bonds between the two through the night elf Highborne kinship and the black moon sect of the priesthood that utilise night warrior void magic, something the void elves would be very interested in about Elune - and may even yield a home for void elf priests. The Elune religion perhaps being the only one where worship of a good deity can allow for use of the void.