My own thoughts...
Major League Soccer will try to reach an agreement for its 30th team to be Charlotte, North Carolina, which could start play as soon as 2021.
www.espn.com
1) MLS is a business and the league's #1 revenue source seems to be expansion fees at this time. The league and its owners have become addicted to this revenue and it's going to eventually bite the league in the arse. It's already impacting USMNT as half the team's strategy seems to be to use USMNT players to market MSL teams, i.e. have nearly every MLS team represented on the National team. I have no issue with new owners wanting it; but, make them work for it like new owners do in Europe - buy a top tier team (without relocating) or buy a lower team and then invest in the team to push them into the top tier via Promotion. Problem is, MLS and the owner's ego can't handle the fact that if they don't continue to invest in their teams, they could get kicked-out via Regulation.
2) The success of Atlanta and Seattle playing in NFL stadiums is the exception not the standard. Charlotte is the 23rd largest metro area (including part of SC) in the country with 2.57 million people whereas Atlanta is 9th with 5.50 million and Seattle is 15th with 3.94 Million. Seattle has always had a strong soccer fan base and finding suitable land at a reasonable price in with public transit access that area is difficult, so putting them in Century Link Field was a pragmatic decision. Atlanta does not have the land challenges, a smaller fan base. Instead, it has an owner in Athrur Blank who bought the NFL Falcons in 2002, failed to buy the MLB Braves in 2007 and began pushing Fulton County in 2010 (Jerry Jone's AT&T Stadium opening a year before in 2009 was not a concidence) to replace the Georgia Dome, which was ancient having been built just 18 years earlier in 1992, with a new, tax-payer subsidized stadium, which resulted in the Mercedes-Benz Stadium opening in 2017. His push into MLS felt like a way to 'sell' the Mercedes-Benz concept the Fulton County in that the venue would be used more (and to increase his own revenue). Atlanta FC and Mercedes-Benz have been a wild success, which si great; but, will the team continue to draw if their performance falters over the course of a few seasons. Just look at what has happened with the New England Revolution. Teppler, who bough the Panthers in in 2018, appears to want to be Charlotte's version of Arthur Blank. He wants tax payers to subsidize a new or renovated Bank of America stadium, which was opened in 1996, for his investment. But, he is dealing with a smaller market, a smaller fan base, and a county government (Mecklenburg) that is historically less open to using public money to build private stadiums (see the history of the Charlotte Hornets/Bobcats). Thus, he sees an MLS team and that $300 Million investment as a way to get what he wants.
3) I actually like Charlotte as I have spent some time there for work and a job interview, which didn't work out. From a business viewpoint, its growing rapidly and is home to some major corporations (Bank of America, Honeywell, Lowe's, Sun Trust Bank, etc.), which means potential corporate sponsorships and suite sales, has a good airport, and while is suffers from suburban spread (and a lack of good pizza choices) while people are just beginning to live in downtown (they call it uptown), it's a 90 minute drive to the mountains (Ashville) and 3 to 4 hours to the beaches (Wilmington, Myrtle Beach and Charleston). Raleigh/Durham has the soccer history and a plan or a soccer-only stadium downtown; but, it's only the 36th largest metro area with 1.94 million people (just ahead of Nashville ironically), it has no signficant public transit network, and while many corpaotions are in the area, very few are headquartered there. Plus, its a college sports town - just ask the Carolina Whalers.