When will this myth die?
Atlanta United’s record-breaking 2017 attendance by the numbers
https://www.bizjournals.com/atlanta/news/2017/09/25/braves-attendance-jumps-28-in-2017.html
As is being proven with Atlanta United, Atlanta would easily work as an NHL market so long as there is stable, committed ownership that is interested in fielding a competitive team, pretty much like any other market. Tampa, Dallas, and Nashville are what a competently run Atlanta franchise would look like. The Thrashers failed because ASG deliberately sabotaged the team in order to favor their preferred Hawks. This has been discussed
ad nauseum here. It was not a failure of the market itself.
As for Philips Arena, I have it on good authority that, even after the renovations, it will be possible for the arena to host a hockey tenant. The courtside bar for the Hawks is fully moveable, and in fact is moved for concerts. I've heard through the same well-placed grapevine that Hawks/arena ownership isn't interested in an NHL tenant, but is interested in the idea of an AHL team in the not-too-immediate future (i.e. two or three years down the road).