"If the goal is a centerfire single action that Ruger can bring to market for the same price, maybe slightly more than the .22 Wrangler, the only answer is .32 S&W Long and it'd probably have to be limited to wadcutter only due to the length."
The same thought struck me. I really like my Single Six in 32 H&R magnum. I haven't compared it to my 22lr version to see what the size differences are.
It would be nice if the Wrangler frame could accommodate 32 S&W long. I see it at the big-box stores from time to time and feel that it's an underappreciated round (more oomph than a 22lr, but not much more recoil).
If not 32 S&W long, maybe 32 acp? It's commonly available in stores, even more than the S&W long. My uninformed hypothesis is that the semi-rimmed case might work okay with a single-action revolver. There might not be much demand for it, though: 32 caliber doesn't seem all that popular these days, and the 32acp crowd might be a very different group of folks than the SA revolver crowd.
I also would like to see 25acp handguns with 4" or longer barrels and decent sights, if for not other reason than it's a more reliable round than 22lr. Can it be loaded significantly hotter? I personally have no idea. If so, it would be fun to put into a little rifle. I'm not Scottish, but I
am cheap. (It has nothing to do with my hankering for new categories of 25acp and 32acp firearms, but it's fun to say.)
Please forgive me for going OT, but the only 25acp pistol that I've fired that was reasonably accurate for me is my Mauser Model 1910. It has a 3" barrel and actual sights. (In case anyone else was looking for something like that.)