I wonder if Sony would have bothered remastering Spider-Man if they weren't already building new (but very similar) tech for Miles Morales. Similarly The Last of Us Remastered was in part a result of the work Naughty Dog did to get their tech working on PS4. In both cases it feels like a case of confluence of timing and re-monetising work.
I will honestly be really disappointed of Naughty Dog spend any more time remaking existing games. They released four new games on PS3 and just two (and a half) on PS4. I want them to make new stuff given their output has halved in one generation. I want them to throw out a cheap and cheerful higher-res 60fps patch for TLoU Part II running on PS5 and move on to something new.
I think it's a bit obvious that the entity "Sony" does not have one rule, since it does not ultimately control what their own studios may want to release. Case in point:
- Ghost of Tsushima, not only had a completely free multiplayer DLC a few months after release, but also a wonderful and completely free PS5 update.
- God of War, free PS5 upgrade.
- Spiderman wasn't free as it was a 'remaster' which actually was quite a lot of work and not the usual uprez+60fps kind of jobby. And it released with a new game, so who knows what happened here.
- ND are silent so far.
- Days Gone, free PS5 upgrade.
- Guerilla games, silent so far, they seem to be quite busy with the new Horizon.
- Japan studios (they made Bloodborne, right?) annoyingly silent. BB needs an update but we all know it's just not going to happen, it didn't even get a refresh for Pro.
There is no pattern, but if anything it looks like there are more 'free upgrades' than paid ones - actually, so far it's just one (Spiderman).
I don't think that looking at what happened in the last generation is any indication of what might happen in this generation - this applies to Naughty Dog, at least.