RNG already has some pretty powerful WSs (sidewinder/slugshot/jishnu/etc) but I'd kinda like to see a WS that can hit multiple enemies. Maybe something like:

Archery
Arrow Storm: Delivers a conal attack to targets in front of you. Damage varies with TP.

Marksmanship
Scattershot: Delivers a conal attack to targets in front of you. Damage varies with TP.

Somewhere along the lines of Fell Cleave/Sonic Thrust.

Most other jobs get access to AoE WSs and it's been something I always thought RNG lacked.