I would like to see that also. Colt has offered a .45acp auxilary cylnder for their SAA from time to time and Uberti/Cimarron offers that option, as does U.S. Firearms and perhaps others. Based on cylinder dimensions, etc., one would think that Ruger could do the same, should they see fit to do so. I have only heard one possible reason given for not doing so. A knowledgeable Ruger person, a gunsmith, on another forum suggested that Colt, USFA, and Uberti use a shorter, fatter cylinder stop which requires a broader but shallower cut in the cylinder. Ruger uses a thinner, deeper stop which requires a narrower but deeper cut in the cylinder. I don't know if this is really an issue or not, since the cut is offset from the chambers so I don't know if it affects the thickness at the thinnest part of the chamber walls. I would have to leave the technical considerations to those who are engineers and better suited to sort that out but I remain hopeful that Ruger might offer some limited runs of New Vaquero .45 convertibles at some point. It wouldn't bother me in the least if they even cautioned against using .45 acp plus P in the smaller cylinder. I would be happy with plain ol' 230 grain .45 acp. They have not produced any Vaquero convertibles since dropping production of the Vaquero in favor of the somewhat smaller New Vaquero.
In the meantime, I will have to be content (and I am) with my convertible Blackhawks.