The Five Tier System
If it's not already intrinsic to PF2, I would suggest we move toward this so there's consistency across conditions & abilities. Simply said, it's having 5 layers to each (or most) statuses.
Examples already in play:
Skill system: Untrained, Trained, Expert, Master, Legend
Death system: Not dying, Death 1-4
Fear system (PF1): Not afraid, Shaken, Frightened, Panicked, Cowering
Items have 5 tiers too and I expect the PF2 poison & disease systems are also similar. Paizo has said there will be numbers alongside conditions already (so yes, they may already have this pattern in mind).
I think this could be applied broadly:
Slow: Not slowed, slow 1 (lose 1 action, -1 to appropriate d20 rolls), slow 2 (lose 2 actions, -2 to d20s, -5 move), slow 3 (free actions only, -3 to d20s)), slow 4 (zero actions)
Perhaps the petrification system uses the Slow track, ending in being petrified instead. Paralysis could work the same way.
Hampered, Entangled, & several other conditions could use this too.
Condition 1 (+/-1 so some rolls)
Condition 2 (+/-2 plus one boon/bane)
Condition 3 (+/-3 plus more intense boon/bane)
Condition 4 (+/-4 plus game changing boon/bane)
I think it'd be cool to see more positive examples in play too.
Example: Heroism 1 (i.e. Bless) might give +1 & cancel out 1 level of fear while Heroism 2 gives +2 and maybe some temp h.p., Heroism 3 might then add another use of a special ability or reroll a save, & Heroism 4 might even give temp Hero Points & suppression of all fear.
Haste 1, get 1 extra action, Haste 4 = Time Stop
Another area this might aid with is when Darkness/Light effects interact, to tell us how far up or down the scale effects move and maybe even up to light that's blinding.
There might even be a way to integrate this with grappling so that only the completely outclassed get pinned in one round (via two critical successes). Choking, rending, constricting, & swallowing whole might be tied into this as well.
I could see this being an easy metric to comprehend before even looking up the specifics; from null to basic effect to bad/good to severe/great to worst-case/best-case scenario.
Just a thought. Cheers.