I think he meant the pilots are interested in having them on mainline property. I highly doubt mainline management is interested, for the very reason you mentioned: cost.

Interestingly enough, if mainline did fly them, they could put a few more seats on them and increase the weight to around 89k I think it is and offset the cost of more expensive pilots and flight attendants with increased revenue. I would be very interested to see what United thinks it could operate them for compared to what they pay Mesa to fly them.