Ben,
I deal with a lot of sRGB images (from other people) that I have to convert to AdobeRGB - this functionality would certainly be nice to have.
Yes, but are these images just tagged with an sRGB profile or have the pixels of the image been
converted to fit within the sRGB color space? If they've been converted to a small gamut color space like sRGB, then converting the image AdobeRGB shouldn't get you a pristine larger gamut image. Some data is lost in the conversion. And if you're going to modify the pixels and save them again (as a JPEG) then more quality will be lost.
-Kirk