Originally posted by Nefrarya:

There are still 3 unfinished biomes left at least. IG has given estimates that it should take them about 6 - 9 months per biome. So even with Mistlands slated for 2022, the final release will probably at least still be another year.

That's a little optimistic.
The three unfinished biomes are:
Mistlangs
Ashlands
Deep North
These alone at IG's current rate of development of one biome per year would mean completion of these biomes in 2024. One also has to consider whether or not there are other biomes yet to be disclosed. The land beyond the edge of the world at the bottom of the waterfalls, for example.
However, that is not all... there is also the end game, the game conclusion.
Therefore, I estimate a final release will be closer to 2025 than "at least another year" :)