Yes, chances are slim. Pretty slim. Last time they mentioned an instrumental was the time of SiT recording sessions, and that turned out as instrumental part of Alexander The Great.
Nowadays they use those instrumental ideas and Steve incorporates them into longer prog pieces. So, if somebody comes with Genghis Khan type of demo, it's probably going to end in a complex song arrangement. They don't do 3-4 min standard songs or instrumentals any more because the way Steve arranges songs is quite different than it was 30 years ago.
So, only chance to get an instumental would be that someone comes with really strong material late in recording sessions, with no more verse riffs / ideas or lyrics left to arrange it in standard song. It could happen, but probably won't.
Today most of their album is done like this : Adrian comes with music, Bruce with lyrics, Steve arranges and fills in bits and pieces of both. So it's really a matter of the whole songwriting process scheme that leaves little room for stray instrumentals. And that process is really successful, i don't think they're about to tweak it.
Oh, and i'd like one instumental on next album. Possibly mid tempo Floydish piece type