I flew through YUL on April 6th but forgot to post the picture. It looks like they've added a barrier around gate 51 and there are agents checking boarding passes to go towards the international gates. I'll be through YUL again in a few weeks and can update you on any changes.

Also, I might have just been too tired to notice but I ended up leaving customs and having to reclear CATSA security to get to my domestic gate (User error since I wasn't able to read the signs ?). Wasn't an issue since YUL was pretty dead but I thought the whole idea of OSS allowed for connections without reclearing security?