I'm not exactly sure if I should suggest for third party mod compatibility here. TA is still very actively maintained so I can suggest there instead if it's not your department.

The Elytra Harness is an upgrade to the original Elytra and it's a bauble worn in the body and not armor. It self repairs and uses vis charge (Thaumcraft's version of an energy source) instead of durability when flying, it's graphically the same except there is a harness texture on the player's chest and of course the item texture. It even supports capes as well and there's particles when you fly with it, you could probably do something cool with that like have it be the same color as what you dyed the harness with (Thaumcraft's particle code is pretty messy though as a heads up).

I noticed compatibility with another Elytra bauble mod and I don't recall any other mod that adds it's own custom Elytra item like TA did so I thought to suggest it. Thanks for the amazing backport by the way! (it's funny because I recently found the mod a few months ago before discovering that there was a backport)