Using your theory, NW would only have a hub @ DTW, and DL would only have on in ATL (with a "gateway" @ JFK). Even if you're one of the people advocating a DL/NW merge, do you think that would be enough? If so, why?
I do believe that DL should close SLC and CVG and focus on its strength at ATL and JFK.
As to NW - I don't see DL and NW merging. I'm a proponent of AA stepping up and consolidating its operations with those of NW. Don't care how. Merger, asset purchase, liquidation auction - whatever it takes. It made sense nearly six years ago when the two discussed an AA purchase of NW, and it makes even more sense today, given UAL's survival and exit from Ch 11.
With the NRT and China rights of NW, a combined AA/NW is perfectly situated to compete with UAL, which I see finally joining with DL (which it wanted to do years ago).
Under this scenario, UAL/DL closes SLC and CVG and AA/NW closes MEM and MSP and probably right-sizes DTW to look a lot more like STL's current schedule. Detroit is an important industrial and financial center, but not every important city like DTW can profitably support a huge hub.
Besides - conventional wisdom is that single-airline dominant hub cities pay thru the nose for their nonstop flight convenience. Pax in DFW, MSP, DTW, ATL, IAH, etc. complain that their dominant airline gouges them. Academics have said that's not really the case in ORD, given the healthy competition between UAL and AA, which helps keep prices in check.
DIA and ORD make sense for a combined UAL/DL, especially since SLC-connected pax could move to DIA and any truly high-fare pax connecting at CVG would now connect at ORD. ATL would still make sense as a southern hub (after all, I see AA keeping DFW, ORD and MIA). UAL really should choose LAX or SFO, and LAX really makes more sense for a hub, given SFO's perpetual runway/weather issues not faced at LAX.
US/HP? As I have posted before - that's a lotta hubs for a somewhat smaller airline. Most of the tough decision has already happened at PIT. PHL and CLT continuing as connecting hubs? Dunno whether that's a recipe for profits. We'll see.