Unfortunately an IS game cannot be an "away" game for both teams. It's simple math. Each week, 16 teams play as "home" teams and 16 play as "away", not counting byes. There is always an equal number of each. If you match up two teams in one week playing "away", then two other teams will both have to be playing "home" against each other. Not physically possible, unless you also move that game to a neutral site.
IMO, the league doesn't really think that much about who is losing a home game, they just pick a game that looks like a good match-up that will sell. The schedule is pre-determined, even to which games are home and away for each team, so they can't just change something to what they would like in that respect. The Vikes/Steelers game is already set as a home game for the Vikes, and always was. I suppose, though, that they might choose a team first and then pick what looks like a good game from that team's home schedule.
On a side note, I think that these IS games will always be either divisional games or inter-conference ones, as those are the only ones set in stone years in advance., by the NFL's scheduling formula. The non-division in-conference games are the ones that depend on how you finish.