The chitinous plating upgrade is a controversial one right now. It makes marines only do 1 damage if the marine's attack upgrade = the ultra's armour upgrade, and marauders only do 4 damage if they are on the same upgrade level. I am a fan of buffing the ultralisk armour and nerfing the marauder's attack as it makes ultralisks really feel -ultra-, but right now It feels like a bit much. I understand the concept of letting the dust settle and letting the metagame figure itself out, but I think it would make a much healthier game if the dust settled around a different kind of chitinous plating.
Terran has 2 solid options vs ultras: liberator and ghosts (I'm not a fan of making ghosts the go-to vs zerg but w/e thats for another time). The problem I'm seeing some terrans have is that, although these are strong answers, it takes far too long for terran to get them, and zerg has a strong window before these answers are acquired if he rushes straight to them. Here is my suggestion: Instead of +4 flat armour, the ultralisks has it's armour value doubled
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With 0 armour upgrades (1 armour), the ultralisk gets 5 armour, but would only get 2 armour if changed.
With 1 armour upgrade (2 armour), the ultralisk gets 6 armour, but would only get 4 armour if changed.
With 2 armour upgrades (3 armour), the ultralisk gets 7 armour, but would only get 6 armour if changed.
With 3 armour upgrades (4 armour), the ultralisk would get the same amount of armour with and without the change (8).
With 1 armour upgrade (2 armour), the ultralisk gets 6 armour, but would only get 4 armour if changed.
With 2 armour upgrades (3 armour), the ultralisk gets 7 armour, but would only get 6 armour if changed.
With 3 armour upgrades (4 armour), the ultralisk would get the same amount of armour with and without the change (8).
Essentially what this does, is nerf the powerful spike the zerg has upon reaching ultralisks, but only if he rushed them. If it is in the late-game stage, the ultralisk is just as powerful as before. This allows terran bio to still be able to do something in the early-late game, but will still eventually need those powerful counters (the ghost and liberator). I do believe this will create a healthier metagame when the dust settles, but I'm open to discussion.