See I'm reading those descriptions and thinking how casual players will be moaning while you ruin them with mercs.
A grid system with numbers and ranges would look cool, but I think that's too much for folks out to have fun. If you experimented with it and could compensate for drop, yeah, that's a cool idea, but you'd make life hell on earth for newer players, especially with mercs.
A marked target would be waaaaaay too easy to abuse when it comes to range. Sure, it could be good for speeding up ranged battles, but that takes all the tactics and skill out of the game. Trial and error, corrections and mistakes are all part of the growing process in GoIO, and I just feel training wheels for gunners will never come off once they're on.