Rogues should be able to sneak attack with ranged touch attacks and touch attacks. It's consistent with PnP and there's really no reason not to implement it. I don't see it being very overpowered. Wizards with a rogue splash will likely get +1d6(+3) situational damage boost and pure rogues might be able to play around with limited offensive umd.

It could give that Roguey feeling to spellcasters. Rogue splashes could use the even small bump to help close the gap from losing out on caster levels. It wouldn't even affect their aoe dps so Pure wizards would still be ahead. Also helf dilly could actually make helf attractive for water savant single target dps.

Most importantly, it would be cool.