The issue with all previous jets in this size class is that the seat-mile costs have not been competitive against the Ryanair and Wizz's of the world. Weather you're trying to fill a plane to MXP from MAN, with FR offering a departure to BGY in an hour, or selling seats to Paris from Doncaster, your costs matter.
The thing about the C-Series is that is has genuine A320neo CASM in a ~100 seat package and impressive range capabilities. It opens all sorts of new markets, Doncaster to the Canaries, as an example, or something like MAN-MXP to be offered twice daily.
Granted, if flyBe were to introduce the C-Series it shouldn't be a direct replacement for the 175/195 fleets, but could open a new direction for the company - one which it would seem to sorely need.