1 - Harpoon gun has an aimed shot accuracy of 110%, with a good shooter and kneeling, it's not that hard to get even 100% accuracy on short range. Hitting at 20 tiles is perfectly doable. That being said, especially if we do see underwater missions eventually, a new harpoon gun (with fast-firing capabilities?) could be interesting.
2 - Isn't that what stun and incendiary grenades are for? Neither damage stuff, stun for low armors, incendiary for medium ones. Maybe a "ghost grenade" that ignores armor/items and does straight up hp damage would be cool once you research deep enough in voodoo/demons.