2 changes I'd like to see going into season 7/preseason 7
Mercury Treads tenacity increased to 40%
Yes I know this is quite a buff but honestly, playing melee champions right now feels like complete ass. I would be totally fine with removing the tenacity you get in the defense tree so that you can take other keystones and aren't forced to take a keystone you may not want just for extra tenacity.
Frozen Heart cost decreased to 2600
In the past I was not a huge fan of this but with CDR being available on several tank and off-tank items, Frozen heart has really lost its place I feel. A decrease in cost would bring it up to par and make it a viable item again. You're spending a lot of gold on mana and CDR for a tank item with now HP and only armor, I don't think the cost decrease is unreasonable.