WARNING. HUGEGANTICMASSIVE WALL OF TEXT. There is no TLDR for this because it covers too much. If you didnt read all of it then dont post. I realized my solution opened up some other problems, but then I also saw some opportunities to fix exisiting issues, so I tried to cover all of those bases. That being said, I could've split it into two posts, but I figured two different threads would be kinda silly since one topic creates the other, and I thought it better not to separate them since things take all of 3 minutes to get buried on these forums.
Alright, so Riot released the trio of tenacity items a few months back so "players didn't feel obligated to get Merc Treads against Heavy-CC teams". I see these items rarely, in part because they are like Ex Calling and Quicksilver in that they give low stats but serve a very specific purpose. The issue here is twofold: first, the items' low stats just aren't worth the slot late game when you can trade in your boots for Merc Treads and get a Deathcap or whatever, since you need boots anyway and +20 Magic Pen doesn't make a difference if you get CC'd to death instantly before you recover. Second, Merc Treads give 35% reduction whereas the other items only give 25%. I thought that they could just buff the Tenacity items so they were good enough to be core, but the item balancing in general is pretty good, and also some champs might have to divert their whole build around a powerful but expensive tenacity item, so that didn't seem very appealing.
My idea is this: make a consumable item that costs about 700-1000g that permanently adds a Unique +25 Tenacity stat to one of your items of your choosing; and remove Merc Treads (I thought with the ease-of-use that comes with this, 35 was too much). This solves the issue of having to divert your build because Mundo can make a Spirit Visage of Tenacity or Trynd can have an Infinitely Tenacious Edge (complete with tasteful name changes). This frees up your boots slot so you can get "luxury" or "offensive" boots without losing the Tenacity; or carrying 50 AP in an item slot when you could be carrying 200 in the same one. And if you add the tenacity to an item like Hextech Revolver, then it will carry over to any item you build out of it, so you'd have a Tenacious Hextech Gunblade. The consumable will add value to the item, so if you need to switch your build up, then you will get some (presumably the standard 75% or perhaps 50% like GP5 items) of the consumable's cost back.
Removing Merc Treads, however, opens up another issue. Now there are no boots with MR, so what about Ninja Tabi, since they have armor? And what boots would tanks get? Of course the first thing I thought of was lumping Merc's MR and Tabi's armor into one boot made for tanks, something like...
Marchers of Resilience
+30 Magic Resistance
Unique: Enhanced Movement 2
Boots of Speed + Cloth Armor + Null-Magic Mantle + 150 or 250g
so 1400 or 1500
I made them so expensive since they give fairly high bonuses for one slot.
This and the Tenacity solution above would also keep Tanks from having to pass up Tabi's armor when the whole enemy team is DPS but they have a lot of bruiser/tanky initiators with CC. I also thought since the dodge was gone I might as well up the armor.
But wait, who do we always think of when we think Ninja Tabi?
That's right, poor Jax would suddenly be without his wonderful dodge. I could've just dropped in the dodge too. But that means that (1) Jax suddenly has a lot of durability as a core item and (2) These boots are expensive, delaying Jax's critical dodge procs until he can afford them. This gave me an idea. Berserker's Greaves are frowned upon as being the worst boot sometimes, since there are so many other good Attack Speed items and you could get Boots of swiftness (or merc treads, as it were). So I thought, what about taking Zerker greaves as they are and adding that Dodge that was removed from PDancers that DPS champs love so much, making...
Greaves of the Battlemaster (I thought Armsmaster sounded too much like a shoutout)
+25% Attack Speed
Unique: Enhanced Movement 2
Might increase the price to balance how good dodge is, however underappreciated (or just not conveinient to itemize for).
These numbers are preliminary of course, you MathCrafters out there can crunch how valueable they are per stat they give; I'm no coder and certainly not a balance expert. Just a simple brainstorm, in the wake of me realizing that I had to get merc treads on Brand because the Spellblade was taking up the spot I needed to put my Void Staff in.