I am also planning on doing slings that scale with the strength of the wielder. However, I'm scaling the damage, not the range. I want to replace Jotun Throwers with Jotun Slingers in the LA, and range 40 would be quite insane, wouldn't it?
It's possible to make a sling with damage -2 and str added to damage. For 10-str human, that's dam 8. Slings currently have dam 7 #nostr IIRC, so it'd be a bit better. However, I can't #clear the existing sling, so I'd have to change all existing slingers if I wanted them to use the new sling, and thus I'm not releasing it yet.