I'm not so convinced that filesystem-compression would be that advantageous or save much on capacity. Games backups, ISO's, BIN's have had blank data removed and already optimized. Like music, photos, videos I don't think they compress well. Maybe if you're lucky you might save 10-20% at best. Maybe. But storage is so cheap. A 6TB HDD would allow you to hold all your PS2 backups and 8TB would allow you all PS1 & PS2.
All this said I would like see how the entire PS1 and PS2 backups go on a compression filesystem. I think BTRfs is the way to go. I think where this would shine is if you have a dedicated VMC memory card per game (8mb) . 4000 game backups x 8mb = 32gb. These could compress 99% considering game data is usually no more than a couple hundred KB. Then again 32gb is nothing when HDD's are selling in TB's.