If the money offered in such a situation by NBCSN is equal to or better than what ESPN is paying, it's a deal.

1) It would be an improvement in ratings over just about anything on that channel, except English Premier League Soccer. It may not be blockbuster ratings in the beginning, but the ratings would be better than what NBCSN is pulling in now, and better than what many weeknight games earn.
2) At this level, the promotional value to these conferences from an association with ESPN is already much less than what a conference like the SEC receives. It can be argued that the MAC has lost as much in attendance/etc. from moving their late season games to weeknight as they have gained in national exposure from MACtion.
3) It gives the G5 conferences an opportunity to move their games off of weeknights and back to Saturday. This provides an opportunity to restore the Saturday football experience and all that entails. This is a huge thing for the fans of these conferences.
4) They would need to work out the streaming details, as they would move away from ESPN3. Streaming is not going away.

We're not talking P5 level money or ratings here. However, if the 5 G5 conferences could make it worthwhile for NBCSN (or CBSSN) to overpay, it could be worthwhile for both sides.