Walk-ins

[GeauxHomeLittleD]

It sounds to me like a more "PC" term for possession, maybe one that makes it sound less harmful and more acceptable to certain kinds of people.

Without a doubt. Once the transition has taken place, it is a straight up possession.

My interest was in the claim that supposedly, there is  an increase in the number of walk-ins/possessions, and that they are becoming better at going undetected.

I haven't been reading any evidence of such, though in this day of instant gratification and guiltless debauchery I have little doubt that FEIGNING possession as an excuse might be on the uptick.