Mojang plans to drop 1.15 sometime before the end of the year. It's supposed to be mainly focused on performance improvements and fixes, with the only new content being bees and some bee related blocks. No changes will happen to the server for the 1.15 update, since the only new things will be the bee/honey related blocks which can be found in newly generated overworld terrain. 1.16 (The Nether Update) is supposed to come out sometime after that, I would assume maybe around the same time 1.14 came out this year (April or so?) The Nether is getting a massive overhaul. No changes will be made to the server, the Nether border is currently 100k and hugely unexplored. 1.17 Is where the mountain biome will be overhauled/updated, and that's all we know about that so far.