Rabbi Auerbachs article this week was mostly about popcorn in theme parks.
I fail to see the issue. The popcorn is no worse than the nuts in Krakow, and significantly better since the machine is used exclusively for popcorn. There is a strong financial disincentive to use anything other than vegetable oil which is always kosher (e.g. in the UK or RSA) or at least almost always kosher (the NK element would be gelatin, which would again be batel). On the off chance that lard or the like was ever uaed, it would be lifgam.
Should a hashgocho give a hechsher? No. But could a consumer eat it? Should I look askance at someone who does?