To me PF1 initially seemed a streamlined version of 3.5, which was why I bought in. For my group, it completely replaced 3.5. We never looked back.
There's been some wanting to go back to B/X recently in that group, until the OSE campaign fell apart. I don't think the nostalgia will be able to bring them back for a second attempt.
This is why I've been saying I'd love to see a streamlined, nostalgia-inspired ruleset that doesn't have the low power levels of OSR. Because when we were gaming back in the olden days, it never felt that deadly. Maybe it was a different mindset, maybe we used house rules, maybe we weren't playing it "right" - but it didn't feel like tripping over your own feet would kill you; it didn't feel like a single kobold with a sling would kill you.
The games back then felt heroic, awesome, exciting. OSR doesn't capture that to me. I love the idea of it, but it's just not there.