You could just "enhance" the current multishot after completing a quest, keep it's cone effect but let the shots line up after a few miliseconds. Like this:
It would keep it's pvp usage but would also be viable to level like a thief.
A cool idea for fleet missile would be to increase it's damage to perhaps 250% and let it pierce targets like Firebird. In contrary to firebird it would only hit people up to 2 times, so dealing up to 500% damage to someone. It would give Archers somewhat it's own niche as a 'sniper' class instead of just some "kamikaze-melee-range-multishotspammer". Seeing as they got the lowest AC of all classes Archers should be killing from a long range imo, why else would bows have such a long range?