If there is demand for frequency at small airports, then yes. Otherwise you run one NB/day on Su/Mo/We/Fri.

Frequency has been important to pax in the current era. How could that change?

1. Economy is so bad that low fares trump all other considerations.
2. If fares are too high, most small airport pax can drive a couple-three hours to a bigger town... that's ultimately the challenge for small (true regional) airliners. The majority of pax can drive to a bigger airport if frequency is poor or fares too high.

If your flight is once or twice per day and will force you to either arrive many hours early or worse sit a hub for many hours to connect, it quickly becomes more appealing to drive to another airport... even 4,5,6 hours.

I think there was definitely a market demand/business case for 50-seaters pre-COVID. For existing jets. The long-term problem was that the business case was very, very weak on the mfg. side if you're looking at clean-sheet new designs. A modern 50-seater is going to have most of the same equipment as a NB, and probably all of the same equipment as a 70-seater... with fewer seats to provide an ROI. You save some money of the actual quantity of raw material used, but the design complexity and the labor is almost the same. A little jet engine takes the same labor to build as a big one, same for all the avionics and other systems. You save just a little labor on the airframe (fewer of the repetitive structural parts).

You could save some money by reducing complexity but that usually means lower efficiency/higher fuel burn... pay me now, or pay me later.