Yeah, i have like 300+ hrs in the game when it first came out and i want to start a new world when all the 9 bosses and biomes are available. But when exactly is that going to be? Mystlands took like 9 months? It wasnt two years but still pretty long. How long should we expect to wait til its basically released?

Good things take time.

Build stuff. Use different play styles. Set yourself challenges. Spice things up with some mods. Or I guess play something else while you wait.