I’ve only played a few mintues to test how well it works, it seemed to be very playable. Of course you are not going to have the convenience of having easy hotkeys in the form of a regular keyboard, but it is absolutely playable.

I've used a controller to play remote play on my phone, and honestly its pretty usable. You could run into some issues with mods I guess, but rimworld being portable will 100% make up for it. I wish there was a rimworld mobile even if it didn't have mod support.