I would be surprised if the next biome was not released sooner than two years.

Iron Gate Studio (IGS) seems very dedicated to squashing bugs. The immediate success o Valheim upon release undoubtedly revealed a lot of bugs that IGS had not anticipated.

Additionally, I suspect that the establishment of IGS led to a lot of business problems for the founder and chief programmer to handle. Legal business, taxes, hiring of additional people, accountants, and the myriad other aspects of doing business require learning how to handle.

My wild ass guess (WAG) is six months to a year for another biome release.