There have been extensive discussions both here on Steam and on the official Valheim Discord. A search will likely reveal them.

That said , if you see mistlands in the distance best to avoid them if you want to keep an older map for the new update. Also, it is unusual for people to "uncover" the entire map although it has been done by many. There will likely be ample untouched Mistlands for you to discover even with fairly heavy exploration of your map.

Worst case scenario? You take your favorite character / items to a new seed, or even a new gen on the same seed. And have at it. Building is fun.