10mm....but I'm sure a .40 version is much more likely.
Just a barrel change and some minor tweaks is all that's needed for a .40.
10mm and .45 are gonna need a lot more work to make it happen. If they come out with a .45 version a 10mm might happen......but I'm not gonna stand on tippy-toes waiting for Ruger to come out with a 10mm.
Unsure how they'd get it to be reliable, but I'd like to see it in .357 Magnum. I have one of the handful of No 1s they mfg'd in 357 in the 1980s and love it. A 357 out of a 16-20" bbl is serious medicine.