As one who recently decamped from SFO to MSP and travels back regularly, I selfishly love this idea. However, I'm not sure if much from the legacy VX product would survive. It's also not a given that DL would retain SFO as a hub, given how few monopoly routes VX has and the proximity of DL's existing LAX and SEA gateways.
VX+B6 would make sense, as (again selfishly) I'd love to see either carrier consider trying MSP and other flyover business destinations as spokes when the combined company achieves economies of scale.