I have similar fears and I've had them for a long time, so I'm glad I'm not the only one who feels that way.
Azshara isn't just an extremely important and immensively powerful lore character, she's also the most built up enemy IN THE GAME. All other big-bads that have been around since Vanilla are dead or defeated.. except her. Void lords and other adversaries came into the picture much later, but Azshara has had a presence for so goddamn long now. She deserves a proper crescendo.
That said, I do think they will do her justice, but perhaps not much more than that. Azshara is easily expansion-leading material, there's just no discussion about that. Not everyone might like the idea but she undoubtedly has the power and interest as a character to carry an expansion and it really sucks that she didn't get to have that role. Still though, I'm hopeful. The wow team has said that they've poured a massive amount of time, effort and resources into Nazjatar and they clearly have ambitions for the zone to test some new things.. BUT I agree 100% with the mechagon statement. I'm super excited for a new megadungeon and for gnomes to actually come into the picture for once, but it does drain resources that could be used on Azshara's content instead. Some people think mechagon might have been meant for 8.1 but was pushed back.. and that seems reasonable, but still.
I mean, if there's anything that I'm actually frustrated about it's the fact that there's not even a dungeon connected to Azshara's content. It's not a necessity, but we've had dungeons connected to raids throughout legion and it sucks that Azshara won't get one. This is THE first time we even get to see real naga architecture and the raid itself only has 8 bosses, which isn't terrible but.. you know, it's also not that many. So the smaller raid and the lack of a dungeon is annoying as hell.
But well, I'm still hopeful. I think they're gonna do a great job and judged on what we've seen so far Nazjatar looks fantastic and we know that the wow team is great at telling stories and making cinematics.. so hopefully Azshara will be presented in a fantastic way. She deserves to be the face of an expansion and she deserves a wider amount of content, but that doesn't mean 8.2 won't be fantastic.