I've noticed most of the life steal nerfs were aimed at ADCs. What impact does this have on sustain supports? Is this being done so they are going to be more valuable a pick? Is this a sign that sustain from supports are going to be nerfed next?
I don't think it will have enough impact early game enough to affect sustain supports. I think the nerfs were aimed toward late game.
I believe the issue is that (early game at least) you either have too little lifesteal or too much lifesteal. The changes aim to allow stacking of Doran's for just the right amount of lifesteal needed based on the lane instead of a straight rush into Vampiric Scepter. Like if you're laning with Soraka, a single Doran's Blade is probably enough lifesteal, and you can start building damage.
I don't think it is enough of a nerf to make a difference. Between the summoner spell heal and healing done by the relic shield, Thresh/Braum/Leona are still going to heal enough to remain a high priority. People severely overlook the relic shield's 40 healing, which is the same as a lv 1 Sona heal. The only champion that might suffer a little would be Morgana, but I think her lack of sustain will be overlooked due to her amazing utility.
On similar note though, I do see a potential nerf incoming to Nami's heal. Her sudden increase of popularity is catching attention and her heal is without a doubt a part of it. I personally feel she is extremely balanced, but Riot doesn't usually see things like I do. Add in the new upcoming support item and Riot is probably going to take action.
