I mean, it is an early access game so by definition it's uh, kind of not finished yet. To my knowledge though, Mistlands just did exactly the same thing (progression-wise at least) as plains did when that was the newest biome addition. Plains boss had a placeholder item to, pretty sure the plains gear couldnt be fully upgraded either like the mistlands gear now, stuff like that.

Seems those are mostly just easy solutions to making sure the long breaks in between updates don't result in the player advancing farther ahead than intended and becoming too prepared for whatever the next update has to bring (as is a ton of us have chests of flametal somewhere, no idea if itll actually be usable as it is by the time they get to ashlands...maybe we'll need a new crafting station for it or something. Point is, its a biome material for a biome that doesnt exist yet and wont for quite a while and yet still players are stockpiling it with no purpose just in case it might one day...they will totally do so with any other wiggle room the devs give to and potentially ruin the experience of that next biome when it releases as a result...yes totally their own fault, but they'd still likely complain about it to. yay, early access).