Not every biome is conducive to base building so I don't really think the Mistlands can be singled out. For example I seldom, if ever, see people postings pics of their sprawling bases built in the middle of the Mountains.

As to gear upgrades the mechanic of needing resources from a more difficult biome to fully upgrade gear (usually via the need for upgraded crafting stations) that was crafted in a lower biome is not new.

Example: to cap bronze Armor you need a lvl 4 forge which will require getting an upgrade that will take either iron or chain, both from a more difficult biome than the one in which bronze armor can first be crafted.

This is not always the case with all gear, but it shows the mechanic is not new to Mistlands in that gear crafted there will probably need a resource from the Ashlands to be able cap its progression.

The hang-up is that prior to the Mistlands we had the 'more difficult' biomes we needed resources from already in the game. Now, with only one biome being added, any gear crafting progression that mimics earlier chains (like bronze) will not be able to be completed until the next biome is added.

Just my take...