I'm just gonna go out on a leg and put all speculation out to shame here because there are plenty of uses for the building and the land itself, but mostly everything has its drawbacks.
I can see the IX being a major cargo holding center for FedEx, UPS, and USPS if they choose to leave it up. Hopkins is more of a Cargo airport than a passenger airport anyways, we see alot of cargo in and out of the area, it would make sense if we had a larger facility for that sort of stuff. Holiday rushes aside.
If they do plan on building more terminals they better acquire some more airlines, it's just not that busy of an airport like Newark, Detroit, or Chicago. However I applaud Hopkins on picking up Iceland. It would make sense for them to demolish the IX and shuttle people over for additional terminals for overflow. I like Vegas' McCarran Intl Airport because they've kept their airport small, and have different terminals on either side of the runways. They use a tram system underground to take you to your terminal, certainly unique.
I can also see them acquiring to demolish, and start a new central point for the airport. Since both are relatively closer to one side or another, I could definitely see different airport terminals for East or West departure shortening aircraft taxi times. This doesn't mean the property from Ford would be acquired, but if so there would need to be some sort of resort, parking, or office space. But Hopkins is never short on parking. Especially on those pay by day lots around Snow Rd which get shuttled to the airport. So what could possibly entice people to come closer to the airport and bring extreme land value to the condemned land. Maybe a business park, more hotels, an outlet mall, an indoor water park, NASA Glenn use, maybe some hangars, an Air National Guard unit, or even a place to put a windmill.
Now there is no way Hopkins would demolish the IX to pave another runway. Having been in the Air Force, it's easy to see why airports are situated the way they are. They use runways depending on weather, and fly into the headwind to help the aircraft take off. If there was a runway that ran perpendicular at Hopkins, planes landing and taking off North/South would be in for one hell of a ride. In our climate, wind and weather almost always wind run West to East if not SW to NE. Very rarely will you get anything from South to North. The only thing heading in that direction would be lake effect snow and the arctic wind stream dip. So if Hopkins builds another runway, it would almost never be used.
There are plenty of things you can do with the IX. As a former aircraft hangar maybe it will return to its roots. It's certainly big enough for depot maintenance; for multiple planes at that fact.