About Meddler's intent on the new Warlord's.
I think it's reasonable to believe that some marksmen might forgo a lifesteal item and take Warlord's instead, though we might not see that initially (or might see it too often if the launch balance is overtuned).
The healing from Warlord's is going to be regular lifesteal but only against champions and minions. That will function against player summoned minions, but won't do anything against wards or jungle monsters.
I have one issue with this. If this is supposed to promote build flexibility, where are the options for other classes? Mages can't opt out of mana/CDR or self-peel (their only defensive tool) and instead have to rely on items (2 for CDR, one or more for mana, though its sometimes included via regen, which is offered), and non-tank supports can't really take anything except windspeaker or thunderlord's, mostly because if you aren't a healer or a tank, there's no option other than thunderlords.
All this would serve to do, as far as your explanation provides, is make ADCs potentially more self-reliant (via itemization) than they already are, since they wouldn't need a lifesteal item. That isn't diversity; either it will be too powerful on ADCs or it won't be worth taking on them because its not powerful enough for how squishy they are.
Instead of using alienated keystones, why don't you focus purely on what the intent is? If its self-healing, allow ALL champs to be able to make use of it, not just a certain class. You already have things in place to counter it, so it wouldn't be broken 
Is there a reason you don't try to encourage multi-role use of certain keystones, like the new warlord's providing something like 
/
's global damage sustain as you drop in health as opposed to just lifesteal? Still restricted to champions, just all sources of damage can heal.
Don't use Vlad as an excuse for this one because he's getting reworked and you KNOW this. You could easily give him compensation nerfs if he became too powerful and it wouldn't matter in the long run because there's an incoming rework anyway. Keep in mind that this is coming from someone who loves to play Vlad and would never even consider this mastery even if it was changed because Stormraider's with Swifties with a 30% CDR page fixes a large majority of his problems that more sustain can't fix.
