Hmm, I don't agree with the healing aspect, though I am all for an expensive, strong scaling tank items that non-ranged AND non-hyperscaling melees could use. For instance, would you really want a tryn, yas, fizz, or jax abusing this item. You gotta be more careful with these ideas dude.
No, if you want a solid scaling high priced tank item for beefy bois like tanks and juggernauts, it needs to have scaling added in there, and not just insane flat bonuses.
How about something like this +200 HP (+.15 base hp +.25 bonus hp)? A rather normal HP build for tanks and juggers with some hp runes would yield about 2295 (i did some simple calculations) Bonus and about assuming about 2250 base HP would yield about 911.25 bonus HP late game. If you're cho with 10 stacks, you'd have about 7,706.25 late game. This of course, only makes the item good after about 3-4 items. As for resists, I'd lower the armor and give it some MR as well (after all, why wouldn't the Emperor's armor be enchanted, as your passives already suggest.
So let's say, 40 armor and 20 magic resist.
Now, you're passive healing is, to put it bluntly, broken. While tanks should have some scaling options, that would nearly make them invincible against all AA or AA-hybrid champs and would be utterly ridiculous if paired with thornmail (even if some counter-synergies exist) and with certain other healing items and certain champ kits.
How about we keep the the AA damage reduction but lower it to 8% (stacking additively with ninja tabi), as that would still be better than the crit reduction from randuins since it applies to the base damage as well, and to all AA's, not just crits. Since this is an item reserved only for brave warriors, how about some form of team fight utility based on boosting morale through exemplary leadership and courage in battle:
Brave Heart: After either 5 seconds in batter or taking 35% of max hp damage in 3 seconds or less or killing an enemy champ, item can be activated to give champion and allies in a 750 unit radius gain: 20 armor and magic resist, 15% tenacity, and 10% spell vamp for the next 5 seconds. Cannot be activated without teammates around, can be activated even while stunned or knocked up. Ally champions with less than 25% hp or mana are healed/restored 5% max hp and mana.
Unique passive: 7% movement speed (this is definitely a good one I think)
This way, you'd have a SCALING lategame tank item, that wouldn't allow the likes of tanksuo or tank fizz or tank ekko to suddenly re-emerge. Imagine even just fiora or jax taking this item. Champs like yas have low base hp, so he wouldn't scale amazingly with that aspect, he also build very little hp if any, so if he wanted to get good scaling from an item like this, he'd need to sacrifice a lot of damage to do so. But tanks and juggernauts would actually be able to build an item like this for some late game scaling and do decently with it. Some champs like sion or cho would likely synergize way too well, but number could be fudged around enough to make an item like this balanceable I believe.
This would give tanks a lot more durability like you want, without making them literally almost unkillable like your healing passive would essentially do.
I mean, imagine a tank with your version, plus titanic hydra, plus steraks/ROA, ninja/merc, randuins/thorn, and some other item for defense or damage? They would literally become nigh unkillable, and do insane damage as tanks, which is exactly the problem we need to avoid. Perhaps even my version is too strong and could be toned down tbh.