Thank you for the very thorough and well-reasoned response to my question.
We think very similarly about these things. Like you, I turn to the Fuji XT-1 when I need versatility. But when the light is good and I am not in a hurry, I still can't beat the Sigma SD1m. I have been disappointed by the Sony A7r but I haven't given up on it yet.
So given my other non-Foveon options, I don't need the more rapid AF and processing speed to the Quattros compared to the Merrills. I still use my DP1m and DP2m occasionally.
I suspect that the delay in the Sigma SD1 Quattro may be a battery issue. Battery life on my SD1m is not great.
If Sigma wants more processing power and live view in the Sigma SD1 Quattro, they will need some clever engineering.
Time will tell...
Thanks again for a great response to my question.