You can make arguments both ways but the arguments against a hub are pretty strong unless CLE demonstrates some traffic growth, or even potential traffic growth.

MedMart is probably the quickest possibility for generating significant new traffic in a hurry.

The sale of ExpressJet probably means the ExpressJet board sees CO/UA attriting their capacity faster than they could replace it with new business - also a negative for CLE.

An argument in favor of CLE is that it is a thorn in the side of DL/DTW and probably 'steals' as much traffic from DTW as from ORD.  If competition heats up between UA and DL, CLE could play a role.  Unfortunately, the point of mergers is to reduce competition, not increase it.