[{quoted}](name=Akali is SO HOT,realm=NA,application-id=3ErqAdtq,discussion-id=8nEdfAtG,comment-id=000200000000,timestamp=2016-11-17T07:08:17.921+0000)
That's a problem though. Buffing or nerfing a champion based on the existence of a stat is bad. An example would be if I nerfed Trundle because there is too much CDR available for him to buy.
That is what happened for marksmen, though, after they got much better access to CDR, and to supports themselves after they had better access to gold. I don't think it's inherently bad to make a class scale with an extra stat, all it does is tie the class's power further into itemization. If the class were, say, marksmen, who already depend on a ton of item-based stats, that might not be so good, but on supports it's probably necessary at this point, since they still don't have any great means of scaling their power with items. Even after the MYMU changes to item-based health regen, there isn't really any stat out there that allows Riot to bind items to supports, which is likely one of the reasons why they're still stuck with cheap items that give them a generic assortment of regen and health/resists.
I think the issue with armor pen is also a separate one: flat pen was changed to Lethality because the original stat gave a huge boost that fell off over time, which exacerbated the issues with assassins who built them. Marksmen were never really intended to build flat pen, but did so in part because they didn't have to trade much off for it, which is why Youmuu's Ghostblade is getting a lot of stats stripped off of it.
With all that said, however, I think there are some effects mentioned in the OP that I don't think would be appropriate to tie to items. CC in general is its own can of worms: having some slows scale with AP is fine, but having all of them scale with items is not, as many mages would then be pushed to buy support items to have stronger CC. Increasing the duration of hard CC is a no-no, as is increasing the duration of effects in general, since that tends to double-dip on uptime with CDR. I also don't think increasing the size of most abilities would be the best, since that could seriously mess with clarity and players' muscle memory (e.g. "why is this AoE twice as large now?"). There are a lot of utility effects out there, though, e.g. heals, shields, various stat boosts, etc., and I think increasing their raw strength would be perfect for enhancing the unique contribution of each support, instead of having them all blend together somewhat once they all purchase the same item actives.