Yea, the pocket door is a challenge, but there should be plenty of room - there should be a lot of space from the door to the ply panel. Once installed, a Molly should only extend about 1cm. Just make sure to cut the screw down once installed (the screw is longer so it can compress the Molly, easy to cut with a pair of dikes).
Optionally, you can use a wood screw for that end, one that’s long enough to just go through the ply when set at the right depth. This will ensure you have maximum thread engagement.
Wood screws will probably be OK, it just makes me a little nervous with that weight. Of course, more screws=more distributed load, but then you have to get them all to line up perfectly, which isn’t easy.
Wow, 50 lbs (~20 kg) per stud, with a bunch of screw holes in the base plate. Problem solved, and you could just use a number of wood screws into the ply panel, just spaced well apart (like 2.5-3 cm), and anchor into a stud where you can with a long lag (3"/~8cm).
Or if you can only hit a stud on one side, use a single Molly on the other and a couple wood screws in between.