Chaos by whom? Changes to the default only affect resource packs when they either open or restrict possibilities. Changes to the actual textures themselves will affect only a few Faithful style packs and absolutely nobody else. So if you're talking about resource packs, I imagine the whole thing will largely be met with a solemn shrug.
As to the internal shaders, Minecraft has had internal shaders for a while now. It just hasn't been properly available for resource packs since Mojang locked it off in 1.9. If they expand the system and unlock it for use... it'll probably still be inferior to Optifine's shaders system so again it will likely be met with polite round of shrugs by most people. A few shader packs might be ported to it, but I doubt it'll be terribly game-changing in the short term.
So yea, not planning for a lot of chaos on this one personally. Sorry.
I don't see why people would be upset when we can change the textures back, if you don't like the new textures simply get a resource pack and enjoy the old feel. I honestly don't understand why they're changing the textures in the first place to be perfectly honest, they could've added an update or worked on literally anything else and that would've been better. There's no reason to change the textures, they're fine.