Indy would be the most likely candidate, possibly using the new layout designed for the MotoGP (I hope so ... the infield switchback was an ugly corner), but Bernie doesn't think there's a circuit that would be suitable enough. Laguna Seca and Infineon are lack adequate grandstands and pit facilities; both would need major upgrades, but the severe inclines and descents mean neither would be considered safe. Portland is simply too short; the quickest ALMS cars do it in just over a minute. After all, the A1-Ring was dropped from the calendar when Villeneuve proved you could consistently do it in about 1min 10sec. Homestead-Miami might be a possibility, but it's a very flat circuit and as short as Monaco; most circuits these days come in about five and a half kilometres; Homestead-Miami is just under four. I'm not really sure about Watkins Glen, but I do know that Formula One left for a good reason tht didn't involve money. It might have been something to do with safety in the era of turbo-powered cars. Mid-Ohio is also a little on the short end, and has an odd layout with race starts being held on the straight leading up to turn four.
Personally, I'd like to see forty laps of Miller Motorsports Park in Utah. It's about two hundred metres longer than Spa, but it's got some great corners in the infield and whoever named the turns had a sense of humour (like Agony and Ecstacy, Right Hook and Knock Out, Indecision and Precision).
