The issue is GenCon cannot expand any further in Indianapolis. That means pricing has to be increased pretty substantially to fix some of the current problems. Hotel costs are already well higher than Vegas, Orlando, Atlanta, or Chicago (comparing room blocks for similar events).
If you had a pimp walk up to you in Vegas you were far off the strip into nude dancer territory. I go to Vegas at least twice per year for work. I've never had anything like that happen. The worst I've had happen is wandering into areas with lots of people smoking (something that is going away there). There is a reason more business conventions are there than anywhere else in the world. It is reliable, convenient, and cost effective. I've had room blocks for conferences in Vegas at Caesar's palace for nice rooms between $99 and $150/night. You can stay at most on-strip resorts for under $150/night. The reason is the available number of rooms is more than ten times what you have in Indy. Flights are subsidized so the costs would be lower there as well for virtually all flights.
Chicago has a much bigger convention center but does have a hotel problem. McCormick does have attached hotels (I've stayed in them before) but it caps out at something like 30K-40K people of attached hotels. Past that, you are looking at having to travel in a mile or so meaning it would be similar to Indy on hotels but you would have ample public transportation.
Orlando has a bigger convention center as well and substantially more hotel space. It's problem is timing. With GenCon happening during summer vacation, they would be competing for hotel space with summer family vacations at DisneyWorld.
Atlanta could be a good sneaky option. They have a bigger center and more hotel space (DragonCon is handled really well for a convention slightly bigger than GenCon).
Going full east coast means more west coast people wouldn't come, though. The same is true of going too far west to LA, San Diego, etc..
Denver doesn't have enough hotel space (I live here) and the convention center is only slightly larger than Indy.
Detroit has smaller convention space and is in terrible shape (the convention center). It would be inexpensive, though. Public transit isn't reliable so all hotels would have to be near the center (there aren't enough there for that).
New Orleans would be harder to get to than most places and would be more expensive. They do have the space and hotels, though. (And having great Cajun food would be a big plus!)
Austin would be fun but their convention space is smaller and less hotels than Indy.
That pretty much leaves Chicago and Atlanta. I'd support either of those or closing admission to GenCon at 40,000 or so and increasing all the prices to allow for a better overall experience (ample hotels, enough space for games without it being deafening, etc.)
I'd say Vegas #1, Chicago #2, then Atlanta #3.
Fred