This is more interesting when you look at the larger 2A SCOTUS landscape. It takes 4 votes to grant certiorari. 5 votes for a majority opinion.
Up until recently, we had two blocks of justices... Gorsuch, Alito, Thomas, and Roberts (more or less) that would likely strike down gun control laws... Sotamayor, Kagan, Souter, and Ginsberg that would likely uphold gun control laws. That left Kennedy as the 5th vote, who we know now from statements from former justice Stevens pressured Scalia to incorperate the "longstanding restrictions" language in Heller.
During that time, the court has declined certiorari in 2A cases. Which made it seem like neither block of justices knew how Kennedy would vote after McDonald. Neither side wanted to move the ball in the wrong direction.
Out goes Kennedy, in comes Kavanaugh who, based on his dissents in previous cases, would fall into the block that would strike down gun control laws.
Now, the court has granted certiorari in NYSRPA v New York. To me, this signals that either one block or the other thinks they have 5 votes to reach a majority (hopefully to strike the law and expand the core of the right to include bearing arms), or the law is so egregious that both blocks are ready to strike it down like in Cetano (MA stun gun case). The Cetano opinion was an unsigned unanimous per curiam decision... they didn't even hear arguments it was so egregious. Considering the court is hearing arguments in NYSRPA, my money is on the conservative block looking to move the ball and strike the law. I think they are going to do it in a big way too, because of the following:
The court has had Rogers and Gould (NJ and MA carry cases) in conference with no relist or denial of certiorari.
The court has had Pena (CA handgun roster) in conference with no relist or denial of certiorari.
If the court wasn't going to decide broadly in NYSRPA, they would either grant or deny certiorari in those cases since they cover different aspects of gun controls (especially the handgun roster in Pena). Instead, the court has held those cases, presumably to remand back to lower courts based on the opinion in NYSRPA.
Denying certiorari in Kettler re-inforces that opinion for me. It would seem that the court is not ready to strike the NFA... but it's also not ready to risk striking the NFA as was the case with nearly all 2A cases appealed to SCOTUS while Kennedy was on the bench. At the same time, the fact that Kettler isn't being held like Rogers, Gould, and Pena reinforces my hypothesis that the court intends to cover enough ground in NYSRPA to guide those cases.