The Longbow of Diana should put a floor on the amount of multishot arrows fired from it, so you always get a good multishot. The floor should maybe even just be set to the maximum possible multishot you can achieve.
The Longbow of Diana should be usable for firing arrows without actually wielding it, but this reduces the amount of multishot you can get out of it. This could be flavored as the bow hovering on its own and magically pulling the arrows from your quiver. The main motivation for this is to bring the Longbow to parity with throwing darts, which require no launcher.
Make enchantments on launchers relevant without making them overpowered by adding their enchantment to damage (because projectiles already add their enchantment to damage): the enchantment determines the likelihood of getting +1 to multishot, unaffected by role or skill. This chance is given as either enchantment/(enchantment + 1), or enchantment/8.
If the enchantment is negative, the same formula is used on the absolute value of the enchantment to determine if multishot should be decreased by 1. If it is decreased to 0, you fail to shoot anything and waste your action.
Monks are given some benefit or ability that enables them to get more benefit out of the ring of increase damage. This could be:
New artifact Gauntlets of Throwing: unspecified base type, adds +1 to the multishot cap for thrown missiles only (not ammo fired from a launcher). When multishooting, only one actual item is thrown; the rest are temporary summoned copies of the one thrown with the same stats, which vanish after their flight is complete.
Add a quiver item. Ostensibly in the tool class, could either take up a new equipment slot, or take up the shield slot to prevent you from wearing a shield at the same time the quiver is equipped. It’s not actually a container, and just “holds” whatever is in your existing in-game quiver. While equipped, it adds +1 to your multishot, possibly +2 if it is blessed but this may make it too powerul.
Also change the Ranger quest artifact to the Quiver of Diana, a quiver which gives telepathy and reflection when equipped and possibly also prevents ammo from breaking, though it can still erode. When invoked, all projectiles on the level that you threw or fired are magically returned to your inventory, even if they’re being carried by monsters or buried or whatever.
It is impossible to multishoot anything when you are fumbling or have slippery fingers.
Crossbows deal more damage than bows, but the multishot bonus is lower because they are slower to reload.
Note a similar implementation in dNetHack, where crossbows always only shoot one bolt but the multishot amount multiplies the damage of that bolt.
If both of your hands are occupied, you cannot multishoot thrown ammo (e.g. darts, shuriken, daggers). You can still multishoot if you’re firing ammo from a launcher.
Multishot cap is halved if you are wielding something in your main hand other than the requisite launcher for what you’re trying to multishoot, regardless of if your other hand is free.
Disable multishot if the player is shooting point-blank.
Allow sufficiently skilled characters to multi-fire while levitating.
Gloves that give a boost to multishot somehow: either increase the maximum by 1, or reroll the roll if it happened to be 1, or something. There’s debate on how not to overpower multishot with an item like this.
Rebalance multishot damage so that multishooting +7 projectiles doesn’t give a massive damage bonus over a single +7 melee weapon. Possibly only apply the damage bonus to the first projectile.
Yumis should be treated as “very well-crafted bows”, and they should allow elf or orc multishot to be used with them (as opposed to the current where you need to use an elvish/orcish bow). The Longbow of Diana’s base item should be changed to a yumi.
