Y'all bitches dumb as fuck if you think Rowlet isn't going to evolve by the end of S/M
What he swallowed an Everstone? That's proof he IS going to evolve. They never needed an excuse to keep Ash's Pokemon from evolving before. Aside from Kalos Ash has always brought an underevolved team to the League and none of them had Everstones. So the only reason they'd even bother with this is if they needed an excuse for Rowlet not to evolve YET.
What's gonna happen is at some point, probably right before the League or some other pivotal moment Rowlet will cough up the Everstone and evolve.

Screencap this because I'm gonna be so fucking right.