Thanks for bumping your youtube here. It is just about the best geek-cool thing on the internet. The time stamp on it this morning gave me double-take whiplash, though. Has it really been a year and a half ago since you did that experiment? I'll be really happy when you get time to get back to the emulsion lab!
There really isn't a reason to go with PET over acetate except for how flat ester films still are after they are subbed. Acetate subs easily and cheaply and relatively safely, at least compared to some to the ideas floated here to sub polyester. The problem with it is that the subbing chemistry/process causes it to wrinkle. You almost have to flatten subbed acetate with heat before coating. Coating thickness is only ~ 7-15 mils and so by default the surface topography tolerance of the film is very, very narrow.
Any chemical that can etch polyester film is likely to cause an uneven surface. Same, of course, for heat. This pretty much defeats the reason for using polyester film. Corona discharge treatment doesn't last long, and can fog emulsion, so (as I understand it from my conversations with Dupont) you want to sub the PET with something hydrophilic immediately after the discharge treatment. Then, that subbing lasts a long time and is emulsion-friendly.
Anyway, what I'm getting at the long way round, is that if the goal is a diy subbed film, readily at hand for an intended project, think subbed acetate. Do you have a project in mind that requires PET?