Thanks for the quick reply. So if I understand correctly, apart from being careful about opening large 64-bit viframes in a 32-bit instance, there's nothing wrong with opening the "wrong" file format? I personally find the 32/64 transition confusing enough as it is without having different filetypes as well...
In order to make this easier to manage, wouldn't it be possible, in a future version, to simply make the amount of RAM required by the instance part of the viframe file data itself (the amount reported by VI or VI Pro in "used RAM")? You could then verify, upon opening the file, if the RAM needed is above the amount that is accessible by the plugin (or simply when a 32-bit instance tries to open a > 4gb project). If you do that, you will no longer need two filetypes, and, which is more, you'll be a man, my son :)
Just my 2c.