After moaning for a while that there ought to be a reasonable quality GOTO alt-azimuth mount that allows you to swap OTAs, Vixen has come out with one that matches the description. Hopefully this is a vanguard, with heavier duty mounts to follow.
H0ughy, I found it when I was complaining loudly in another thread and someone pointed it out to me.
Robert, I agree about the limited load capacity. I'd prefer one that was capable of taking heavier OTAs (although even the options for this one seem respectable). I just hope the idea of a GOTO alt-az with a standard dovetail takes off. (I wonder if there could be a way of balancing the OTA on top of an alt-az mount, something that didn't require fork arms or a counterweight system...)