I wonder if the low sales talk is based on vgchartz. Atlus staff have mentioned a few times that their figures are far, far off. Even if it holds some ground for comparison, their figures don't take into account the digital sales of the game (KOF13 wasn't released digitally until several month after its physical release). AFAIK, the Japanese sales figures are the only solid numbers we have right now.
In any case, I hope SNK's commitment to the FGC community, the new graphics patch, PS4 price drop, and an eventual Steam release maintain the game's sales over time.
As for their next game, it's definitely a new Samurai Shodown (unless these are all mobile games).