THIS- I honestly think it's even still a little too early to make the call on PS2 and OG Xbox... these are systems not even 20 years old yet, and it seems like prime time for nostalgia is closer to the 25-30 year mark. Right now is the window for PS1 to try and knock Nintendo down a peg, but the Big N's got their nostalgia game down pat, & I'm not sure the PS1 classic on its own is gonna cut it. Plus, I feel like the PS1's window is a little off due to all the backwards compatibility- heck, you didn't lose it until the PS4 came out! It's hard to build nostalgia for games you never had to give up. As a result, I kinda think PS1 and PS2 will end up 'hitting' around the same time. Even though you could still use PS1 on PS3, it wasn't terribly well advertised & given PS2 didn't work I think more people made a clean break then.
At this point I don't believe there is a set amount of years for a console to become nostalgic and people focus on collecting for it. I feel like what happened is the NES, Genesis, and SNES really kickstarted the video game collecting craze, and as soon at it become too expensive and difficult to collect for these systems, or people found all the games they wanted for these specific platforms, they moved on to later systems that weren't as hard to collect for. I don't think there is a huge group of future collectors that are sitting on a nostalgic time bomb that will go off in another 10-years for the PS2 or original XBOX, I think most people who ever wanted to collect for them have already began to do so. Of course I'm basing this on what I've seen, but I think Gen 6 was definitely old enough to where nostalgia has already hit its stride and it was roped into the retro video game collecting craze regardless of whether people feel gen 6 is actually retro or not.
I feel like gen 7 however was still seen as modern, and therefore its day in the collecting spotlight has yet to come for the majority of people. This also begs the question if gen 7 will ever become heavily collected like previous generations for many of the reasons people have brought up. I personally believe it will, but I doubt it will ever reach the peaks that the NES, Genesis, SNES, N64 Saturn, and many of the other older consoles have reached, not even close.
PS3 I think will fare a bit worse, due to being overall less popular in the day, and- more importantly- remasters. So many of the big games on PS3 have seen PS4 collections & upgrades that it's going to hurt its chances for viability in the retro scene. Unless there's a hefty bunch of hidden gems & exclusive b-tier titles to be discovered later on.
As someone who has collected PS3 for several years now, I can tell you that the PS3 has an amazingly rich library of unique, interesting games, way more than the 360, that's for sure. I'm not saying that out of spite, just simply because I also have collected for the 360 as well and there are far more interesting, unique, hidden gem, and quarky games for it than the 360. On top of that there are a lot more exclusives for the PS3. I think the PS3 will enjoy a much more vibrant collecting scene than the 360 in a few years because of this and some of the reasons I mentioned in my original post.