Energy based ADC?
I don't know if it would fit into the lore or into gameplay since I'm just a casual player, but I think a energy based ADC would be cool especially since the ninja/Asian motif in League is neat. Essentially the champ would have a really large attack range, maybe a slower attack speed, little escape since it would be so long range and his/her abilities would be very bursty or hard-hitting. I know there are a lot of bow/arrow or crossbow/bolt based adc's but I think this would stand out a bit.