Just as a quick aside;
for TV I’ve actually seen a couple of specs from networks requiring PT sessions to be delivered along with all other media. One ‘type’ of spec is very light on details and simply says to deliver mix and stems in a PT session. It doesn’t actually say that the PT session has to be the mix, so it could probably be interpreted as the mix files and stems laid out in sync with picture in a PT session - i.e. no automation, plugins etc (but routed properly of course).
The other spec I did see however was pretty specific in that the mix itself, i.e. all plugins and automation etc would have to be included. In other words one would have to have the mix done in PT and delivered as such. However, I can’t help but wonder if what they really want is “the mix” as done by the post house saved in their archives in case they have to go back and fix something, and that it won’t really matter if they have PT or Nuendo as long as they can go back to the post house. It would relieve the burden of archival from the post facility essentially. Of course, if it says PT then that’s what has to be delivered, but I wonder if there’s a way to deliver something else upon agreement. After all, I doubt that these companies will themselves retain DAWs that are backwards compatible and contain all needed plugins to restore the session…
Anyway, I know that was for broadcast and not film, but I thought it was worth noting that deliverables also vary a great deal in how specific they are on this issue.