On the original roadmap, transmog and gear dyeing was planned for season 4, along with skill sigils. As you know, the latter has been delayed til whenever the expansion comes out, but transmog was completely left out, and there doesn’t seem to be a single dev response as to why.
I know this ain’t news at this point, but it seems baffling that such a simple feature is not only not included 2 years later, but they can’t even be bothered to acknowledge it. It’s not like the MTX are raking in the dough, cause they even said they aren’t.