make it only directly targeted abilities. Having it happen on indirectly targeted (and therefore reasonably dodgeable) abilities would probably be pretty lame collateral damage for other lanes/champs, especially since most melees are reliant on indirectly-targeted abilities for their own poke (especially versus ranged champs). Most abusive ranged vs melee issues in lane arise from ranged directly-targeted abilities and attacks (against which melees can't utilize the only counterplay direct-targeting has, "stay out of range"), and melee directly-targeted abilities are generally combo'd with autos and would draw aggro anyway.
There might be some indirect abilities that should get aggro-drawing treatment as well (Glitterlance, for example, as its speed and hitbox and minion-piercing ability renders it very difficult to dodge; or possibly Morde's E since it's effectively undodgeable through the victim's efforts due to instant travel time), but initially at least just the directly-targeted ones should get the aggro-drawing treatment.
It'd also help if minion aggro calls were increased in range if the source attack of the call-for-help was ranged, as currently ranged champs can even auto-attack while only provoking calls from a few (or even no) minions due to their faraway positioning from the wave, while a single melee attack will generally provoke calls from every minion in a wave since the melee will be forced to be closer to said wave.