Weird that Google never found that thread before during my searches. Thanks a lot Gameblabla. I knew about when the device came out and was convinced that the games were not stored inside the computer, but the fact it's really a 8-bits computer that actually had Playstation Now capabilities and the fact it was online (albeit via a cable signal rather than Internet) makes it even more amazing to me.
As for why those devices are rare, I don't think it's just because people had to give it back to Vidéotron when they unsubbed, but also the fact that once the service went offline in 2006, those devices pretty much became paperweights.
As for why the device hardware was made so hard to open up as shown in the pictures posted later in that thread, I'm 100% sure that it was to prevent Bell Canada from copying Vidéotron's ideas and release a competing TV service + terminal.
Anyway I wish Vidéotron decided to convert the analog data to digital and release some sort of Videoway emulator on which some services would be disabled, but games would still work.
EDIT: I'M reading that in order to retrieve the games and possibly emulate them or convert them to a different playable format, just a good VHS recording of the beginning would be enough.