jsloan

CLE made little sense as a hub for CO and makes no sense at all for UA -- it's just not far enough away from EWR, IAD, and ORD. The only possible purposes it could serve would be as a reliever hub, drawing excess capacity when the larger hubs are full -- but they're using IAD for that purpose -- or as a defensive move, but neither AA nor DL would really benefit from a CLE hub either, for pretty much the same reasons.

The biggest hole in UA's hub system is the southeast. However, it's hard to find an attractive southeastern candidate for a hub. Atlanta would have the right spacing, but I can't imagine ATL needs that much more capacity, and I don't think they'd want to pick a fight with DL (even assuming they could get gates). Jacksonville is the largest city in the region that's not already a hub for somebody, but it's extremely southeast, to the point where it might not be much more convenient than IAD.

FWIW, I think DL is hubbing RDU as a defensive measure against UA, but I can't see UA wanting RDU anyway; it's just not far enough away from IAD.