Let's be honest. This sucks. Completely. You give up your armor proficiencies, and you need to be able to wear heavy armor in the first place to get this ability. Plus, if you ever cross-class into something that doesn't get heavy armor, you can no longer progress the armor bonus. That, sucks.
So this is my take on it. For the most part, everything stays. You still need to be of the dragonblood (subtype, actual half-dragon, dragonborn, etc). You still lose all armor proficiencies for taking this. You still grow scales in the same color as that of your parent dragon. However, it does not take no eight hours to grow. It will instead take a little longer than it would to don heavy armor without help, so about 10 minutes. As for shedding, it'd again take 10 minutes. It is a lot of scales, and it's what it was originally.
Scaled hide will still be AC 6 + 1/3 class levels with heavy armor proficiency (+7 at 3rd, +8 at 6th until +12 at 18th. Still get energy resistance 5 every five levels from 5th to 20th for resist 20. It will still count as a set of medium armor that's -4 check penalty, but have it as a +3 Dex modifier for maximum. Make it the equivalent of a set of breastplate and scalemail for Dex bonuses. There's still no arcane spell failure.
However, it's here where the real changes are. While at 1st level it'll count as medium armor to make your speed 20 ft., this will change at 4th level. It is at this point that the character will automatically gain the Pathfinder's armor training ability that the Fighter gets. This allows you to move at your base movement instead of the reduced one, will increase the Dex by +1, and reduce the armor check penalty by 1. This will continue at levels 7, 11, and 15, making the husk 30 ft, +7 Dex, and +0 ACP. This is of course assuming that all 15 levels are from a class that's got heavy armor proficiency.
The problem with a dragonscale husk is that it's not clothing or actual armor. So this makes it impossible to have magical vestment placed on it. I suppose a feat could be homebrewed to make the scales only take 5 minutes to grow and shed, and even allow them to be imbued with magic. Maybe even one to harden the scales giving it adamantine properties for DR 3/- or lightening it like mithral to give +3 Dex. Kind of like the feats warforged have.
If this is used for a Pathfinder game, and the actual Pathfinder Fighter is used, the PC can instead use a substitution ability for the fighter instead.
