I disagree about Earthen as an Allied Race and Dragonriding-- Dragonriding outside of the Isles was always going to happen, and the Earthen as an AR were designed specifically to be an AR. I think they did a great job with Earthen culture and I like playing one. I know it's just yet another dwarf, but it was already a big part of the expansion, it seems easy to add on.
I do agree we should have gotten a tinker class, but I just don't know why we didn't. My only theory is that we'll get Tinker as Articifer in TLT with it being Titan themed and racially agnostic.
Zuldazar was updated and expanded and I believe is confirmed to have a second entrance for Undermine. There are stills of a cinematic with the drill in Zuldazar, so I have to imagine part of the intro questline will take us there.