We both misunderstood each other, thankfully. 
I thought you meant Shadowlands Pathfinder wouldn’t be account-wide, which is why I said what I said. Apologies. I need sleep.
The blue post says you will only need Expert Flying at level 30 to fly in Draenor and Broken Isles, per toon, instead of Draenor Pathfinder and Legion Pathfinder. If you already have the achievements, that doesn’t get taken away. And if you want the perks of Pathfinder, (mount, riding speed), you can still do them if you want.
When I said any toon at level 60 on an account that has unlocked all three Pathfinder achievements, can fly in current Pathfinder zones, (levels 90-120), I wasn’t referring to Shadowlands, because it will obviously change due to the level squish.
The incentive for doing Pathfinder is the account-wide unlock. Taking that away in Shadowlands would likely cause players to bench their alts, unsubscribe in between patches and play a different game, rather than have to re-earn Pathfinder on every alt they have