So, Riot already anounced they are looking intoand want to change it a bit. Here is what I would do.
I think many AD Casters would like that, already thinking about :D. And yeah, unique armor penetration, otherwise we would have League of Reavers. (Offers the same stats as , just even better lol). Also, the combination of good AD, life steal and CDR is a strong and unique combo, so kick out the CDR on the one-side bench as well.
I think about making the life steal also avaiable to single target spells, but that would probably be totally broken, well. Maybe something like that it applies 1/2 of the users life steal on every single target spell physical damage. This would be only for, of course. It would then also up the cost to like 3500.