I'm not sure the heat will be that much of an issue. It's going to be hot wherever they play in July unless it's like Australia. I don't think it would be Qatar hot but it's going to be hot for every team there.
As for the ATL, DAL, HOU stadiums, I believe they all have retractable roofs so they can bring grass in like they have before and if the roofs are closed during the hotter days they have matches, I doubt it will be a big issue.
I would have liked to have had them come here. I was always curious about where they were going to play besides TQL.