If there is enough demand to fill the plane, and you can get some C or even F pax onboard, it's probably fine. The 737 fuel burn is low, so a small plane like that is probably the only way to make a route of such distance and low demand viable.
If the demand is only 120-200/day, you probably will not get a miniplane warning or penalty. And you probably won't have widebody competition because the route is too small to support a widebody.
737-700ER, with the tweaks to the system, will be ok on these routes.
To make them viable, however, you need to do 3 things:
1. Own them. Lease 737-700ER's are about as good as Concordes.
2. 7 day schedule them to get every last minute of flying time out of them.
3. Find routes that can support at least a 5C/114Y config, and preferable a 3F 15C rest Y config (not likely if we are talking about routes with 100 daily demand).
They will not make tons of money, but if you have cash to spare and are looking for a unique aircraft to play with, the 73G ER fits the bill.