Hang on, Prophetic aim allows the Warleader to not hit Allies on a Despair, so that Despair could still be used to hit a different NPC. It also says nothing about not upgrading the attack, so the Warleader is still getting an Upgrade.

Yeah, blow out the lights, set something on fire, set off the fire suppression system ("By the way, that's a halon system. Looks like everyone in the room takes your rolled damage in strain") - any number of reasons that you could upgrade the next check without damaging your friend.

That would be a "miss", IMHO. If somebody succeeded with a shot, even with a Despair, it means they still hit the target. I don't think it's fair to take that away. But remember, one turn of shooting isn't just one shot, it can represent several shots...one of which, unfortunately, hits your friend.

This. I don't think despair takes away your success. I narrate it as either your flurry of shots hits your intended target and unfortunately your ally or your shot tears through your intended target and also hits your ally. Keep in mind combat isn't 6 second rounds like D&D. I often remind my players the combat is a sequence of exchanges of blows or fire. You might fire of several shots before having a clear line of fire at your target.

You can narrate the despair as: As your wookie ally swings his vibroaxe at the stormtrooper sergeant you line up the perfect shot. Just as you squeeze the trigger the sergeant uses the wookie as a carpet shield absorbing several blaster bolts before your shots also strikes the sergeant in the chest and shoulder. Both take damage of X.

The fact it just hits anyone engaged with the target and not specifically your ally is why I think RAW is fine. Your shooting at the Nemesis and roll Despair? Sorry buddy but those minions keep getting in the way and take the hit, thankfully it wasn't you PC mate.