Quite simply: this would be like .mptm - with the exception that the samples are not saved with the file, but dynamically linked to .wavs (or proprietary sample format) on the hard drive in a specified (relative path) location.
This way, you could save a large number of versions / version history of your song project without filling the HDD space by saving multiple copies of the sample data with the patterns.
I know there is already the Impulse Tracker Project (.itp), but it doesn't work properly if the same sample is used in multiple instruments, which I tend to do a lot to get more different uses out of a single sample. Also, it doesn't support the other advanced .mptm features, like custom pattern timesigs or multiple sequences.
Is this technically feasible? I know at least that .wavs cannot store all metadata required by OpenMPT in their header (such as, whether the loop is ping pong or not) so that data would have to be retained in the .mptp. Loop points may also have been modified inside .mptp to get ping pong working, so the loop point data in the .wav would have to be ignored when loading the song, if this has been done.
