Personally, I’m most excited for the dimensional planes in the far future–lots of opportunities for unusual gameplay variations. They sound perfect for @Vince5754’s Magic Biome and Magma Frost Biome.
One biome that would be interesting to me would be some sort of Petrified Forest. These rare, unusual (and large)trees could mix the game up by providing stone instead of wood (or a combination of the two?), plus occasional ruins or explorer camps. The trade-off could be having to survive the giant, ancient creatures roaming the remains of the massive woods. Think of it as an alternate challenge biome with greater resources and greater enemies. Maybe the only way to survive at first is to build upwards into the trees and stay above the surface enemies below.
(And yes, definitely, to restoring and settling old towns and ruins, @Spododo!)