Sweet, that's one of those things I've always wondered why they didn't already do (same for DF, even if Animal Type Good has a little bit more memetic status in the DF-sphere). It seems it would be less convoluted to have like, 3-5 different kinds of leather, depending on say thickness, and then however many special case leather types one might add to that.
I see that as dumbing down of game mechanics and complexity, which tends to result in "masterpieces" we've been having lately.
But on the flip side, what particular actual gameplay is gained from having 12 different types of leather that all have the exact same stats across the board but different names? If anything, it's a bit detrimental in that they clutter up storage due to an inability to stack and make it arbitrarily more difficult to craft because you need the same type of leather to make items: you can't make dusters out of both bearskins and elkhides even if they have the exact same properties. While 12 is the outlier, there are several other groupings of 5-7 leather types that don't introduce any sort of advantage from a position of gameplay, verisimilitude, or realism that are perfectly reasonable to condense, and even more if you loosen the borders slightly to allow differences of around 0.05 in the multipliers. This isn't a slippery slope: a large number of identical items in the game that do nothing but clutter up stores and make it impossible to craft for no other reason than game mechanics does not make the game "smarter," nor does condensing them based on their actual properties rather than their names automatically make it "dumber."
I dunno, but it might be weird to hear that coming from me since apropos of the recent conversation on Combat Realism, I actually keep ammo turned on in that mod to juggle different ammo types and calibers. There, the different items do have gameplay effects: you can't load different caliber munitions into different guns, and different payloads like AP, HP, EMP, incendiary, and so forth have different effects, making it worthwhile to rationalize munitions production and ensure you have the right load-out for your expected foes. I do like the idea of the leather change, but I haven't tried the 1.0 beta since I like my present mod set.