there are console commands to genarate added content to old worlds and the dev has stated they dont know yet what the impacts will be on old worlds

i had explored all of my map i have used the dev command GenLoc to spawn the tar pits into my game for were they are seeded .

There's also at least one mod for rolling back explored map areas that will likely update to deal with whatever happens in the new biome. Probably don't build there though, the entire geography could change.

There is no precise ETA for the update, which doubtless means it's not coming anytime soon, which in turn means you'll have plenty of time to "finish" the game in your current world. And then you can just start a new world once the update does arrive, without losing all that much.

That's what I'll do, anyway.

(Mistlands is, in a way, less empty now than it was prior to the update yesterday. My outpost area had been affected despite being a previously discovered area, too, and now looks rather cool. But also creepy.)

You should go where ever you want to. Game's in Early Access so your world is gonna get outdated no matter what you do. No point in limiting yourself, you might as well go see it if you're curious

Anything you walk into may not change/update later. See the H&H example of tar pits only spawning in new never seen before plains, not your old hunting grounds.

however a DEV or dev rep said that you should expect to start over at game launch if not before. So some future patches may totally fail on old worlds anyway.

So, you can explore some of it, but it may not update properly later. Leave most of it be, seems like a better idea.

Do what you want, exploring one mistlands area isn't going to ruin your game, there'll be a whole lot more on the map.

From the October dev blog https://steamcommunity.com/games/892970/announcements/detail/3061877729280651185:

It’s also still too early to say what the implementation of the Mistlands will mean for your existing worlds, but we will keep you updated once we know more.

its just empty biome.you can go, nothing to hurt you

Nothing to hurt you, but it was said somewhere that exploring those areas before the update means they won't generate the content. Only unexplored areas will generate the new content.

Any lands explored may not be updated to the new content. For that reason alone you should not explore the mistlands on your favorite map unless you want an empty safe area to build in.

I'm personally only going to explore 1 mistland spot on my map and not explore the others just to have one unique area.