Yes, majority of my current island is unterraformed!! It's the challenge I set for myself when I restarted my game, I realized so much of my time has gone to planning my island as a whole that I tend to get so burned out just by thinking about the map
The theme of my current island is something like "overgrown city" so literally the mess is part of the aesthetic.
This is my current map! The colored area are the areas I've pretty much finished decorating. I've terraformed a bit here and there but nothing absolutely major, except for the river at the northern most part which I had to revamp to make room for a stairway downwards to Redd's docking area. I know there was one other area I terraformed quite a bit, but this was back when my island was so new that I didn't have a theme yet, and there was a decorating event that made me mindlessly chip away at a cliff area for some picture. It's not super noticeable on the map, and I didn't really re-terraform that area after the TBT event, I just left it chipped away and worked with whatever was left.
Even the rocks, I refused to break
as you can see here, I ended up leaving one rock in the middle of the road and another behind the caged bar to the right.
I have also not moved any of the villager houses since plopping them down!! Here are two of the starting houses hehe. Definitely tried working around their weird placement.
Overall, I'm having fun with decorating! I edit the island a little bit here and there, but again nothing too major. I really want to keep this map layout and not worry too much about terraforming <3