TNA will struggle to secure MSG, since it's heavily dominated by Vince.
I'd like to see them in the New York market for B4G, and run the Hammerstein. Cram as many fans in there as possible and provide a real epic atmosphere to the show.
As for Slammiversary, I'd nominate Nashville, going back to their roots and all. Would make the spectacle of the 'anniversary' feel a little more significant.
I would rather see them try Huntsville then try Tennessee again. Tennessee was horrible during Lockdown.