My two cents, FWIW.

The increased capacity to increase LGA operations is going to have to come from somewhere, even after factoring in moving a few DCA RJs up to LGA. That somewhere will likely be CVG if DL doesn't want to increase overall domestic capacity. CVG's days are numbered, though it will continue as a focus city with flights to the largest business destinations.

MEM will probably be next to shutter, but only after the new terminal at ATL is built, giving DL control over all of the current complex. With the opening of the fifth runway, the runway situation at ATL isn't as bad as in years past, and ATL could absorb MEM's passengers. AA kept the STL escape valve around for a few years before consolidating at ORD when feasible.

MSP has been pruned a bit recently, but that was partially due to the temporary runway closure. It might shrink a bit more (especially on overseas flights), but plays a major role in connecting traffic from the East Coast to smaller cities in the Great Plains, Pacific Northwest and Western Canada - something that would be more difficult to do from DTW and impossible from ATL or SLC without major backtracking for many.

DTW seems poised to become DL's Eastern US-Asia hub. It's better located for connections from most of the eastern US to Trans-Pacific flights than ATL or JFK, which would involve backtracking. It might pick up a bit of CVG's traffic, but otherwise will be fairly stagnant domestically. I don't think Michigan's economy factors into things as much as some think, as DTW's main purpose will be to connect people from the Northeast and Mid-Atlantic to points west. DTW O&D traffic is gravy - and, despite its recent woes, Detroit is still one of the top 12 metropolitan areas in the country.

NYC (LGA/JFK) will grow, largely due to the LGA slot swap. JFK should remain stagnant because of slot controls, but we'll likely see many short domestic flights move to LGA and more international and long-haul flights at JFK. Neither LGA or JFK are expected to be major connecting hubs, except to a limited number of flights to Upstate New York, New England cities and perhaps Canadian preclearance cities at LGA and from the Northeast, Mid-Atlantic and Midwest to Trans-Atlantic flights at JFK. Both are really O&D hubs. DL is growing there because that's where the O&D traffic is.

ATL will remain the heart of DL, with more flights than any other hub. It will also continue to be the focus for DL's Latin American operations. It may lose a few trans-Atlantic flights to JFK and trans-Pacific opportunities to DTW, but will otherwise continue to grow.

SLC should remain pretty much as is. It's an important hub for inter-mountain West travel - and flights to smaller West Coast cities.

NRT is interesting. With the new Japanese open skies treaty and advent of the 787, DL's operations could be scaled down there - especially if JAL enters SkyTeam. In fact, the US Justice Department may force DL to divest of some NRT slots (likely to AA) in order to get antitrust immunity for any JAL joint venture. If AA wins the JAL bidding, I suppose DL will have to continue the NRT hub until it can reliably overfly it.

AMS and CDG should remain the same - DL "hubs" in name only run by another airline.