Townstones come out of mystery boxes
Even though townstones can't be picked up after there placed, it could come out of a mystery box and maybe you can make it so that only if it comes out of a mystery box, you can pick it up. After that, it's normal.
picking up townstones, sim9 would HAVE to recode everything etc. and it would be too much work. He could just make a box with a townstone inside of it. but yeah townstones were purposely excluded not just cause they cant be picked up but also cause it wouldnt be an item noobs should own.
If towstones were added to mystery boxes we would have TONS of towns filling up the wild, also they would mostly be crappy towns made by noobs who skipped the tutorial