I see them all the time around here, especially with multiple HVAC system zones. 100A sub panel to feed two heating sections in heat pump installations is fairly common in larger homes to feed backup heat.
I consider such an installation no different that the requirement to have a disconnect for the equipment anyway. Isn't a disconnect essentially the same thing as a sub-panel for the most part? In the instances that I encounter, this is just a case of these disconnects being contained within a single enclosure.
