Signs I'd be looking for:
- Rules Bloat
- Experimental Books
- Growing complaints from fan base around rules
I dunno about on Earth-72, but here on Earth-616 this is already happening. Whether that means Paizo is up to anything, I have no idea.
More seriously, I think it's going to be exceptionally hard to tell if Paizo has a plan for a new edition/revision for now. The company is in a very unique position, probably more like WotC in 1999 than any prior versions of itself. (It's not a perfect comparison, so don't read too much into that one.)
Paizo been around for, what, a decade now? They were a small-time RPG publisher doing well with a big-time contract up until 2007; after that fateful year, Paizo's role changed completely. They transitioned to underdog-challenger, and by 2011 they were the new market leader. Given that their core product line was spawned from the discontinuation of another product line by another company, Paizo has to acknowledge that many of their players are people who
didn't want to change to a new edition. Paizo is now in a position pretty similar to the one WotC was in in 2005/06; they've produced enough Pathfinder stuff by now that they have reach further (either in terms of products or customers) to sustain their revenue. (One consequence is that Paizo is now guilty of producing a lot of the same kinds of products that Paizo fans used to criticize WotC five years ago.)
The real question is what happens now. For all of Pathfinder's success, D&D is still the most recognizable brand (despite not being the top-selling one), and WotC is on the cusp of releasing the first new edition since the one that Paizo dethroned. 5E is already being much better received than 4E was, and can be considered a direct attempt to regain their dominant market share. If 5E is a success it could be a huge blow to Paizo, so for the time being they'll want to focus directly on retaining their customer base; this likely means producing more of what PF fans already like, and very little gambling with new systems.
Ask again in a couple years.