Here is my pessimistic take.
March: Patch 9.0.5 with a little more covenant content peppered in
WoW TBC announced for April launch.
Patch 9.1 announced for Spring 2021. (June)
Since they have great data on how Classic launch saw a surge of players returning to play it. They can leverage the strength of TBC to hold players over while they work on finishing 9.1.
Optimistic View:
TBC and 9.0.5 Launch Parallel in March.
9.1 Announced for End of April.
I imagine they’ll announce extra customization options as they did promise they were working on more. Hopefully they’ll announce them for allied races
They’ll talk about flying
maybe a new zone
nothing exciting as usual at least not for wow cause i don’t care about rehashed garbage content like tbc. all i ask for is new great content and they ruin everytime, there’s not much they can do nowadays or say to get me really excited. shadowlands still needs so much work it just happening at this point.
I could see a Classic BC announcement but I think the actual launch would be a ways out. At most they might have the beta by then but that’s still pretty iffy, in my opinion.
Two words… “Playable Tuskarr” 
Sadness. I predict sadness.
Yup, TBC would be announced on April Fool’s Day. And Shadowlands Classic would also be announced. Why wait for Shadowlands Classic when you can play Shadowlands now?
All I know the TBC announcement is going to intense as fresh servers or even transfer toons over is going cause drama. I’m very interested to know thier direction though I feel fresh servers will increase the life span dramatically.
Just 9.1 stuff mainly. Talking about the story arc, new features and what goes on. Then at the end maybe like a cryptic image to hint at a theme for 9.2.
They may just start the 9.1 PTR soon after Blizzcon. So it could still release around mid-late April or early May. Especially because they’re splitting it up. 9.0.5 is covering balancing and system fixes, so that’s less stuff for 9.1’s testing to do which is a different ballpark of actual content. We’ll see!
A Classic BC would never come out in April or any time this spring. That would require a bigger beta testing and I could see it release either end of this year or during the next. If it happens.
Expecting TBC beta announced to start within the month, with planned release being April/May. Expecting 9.1 around the same time, with us seeing some sort of teaser for it at Blizzcon.
9.1.
Maybe 9.1.5 (Heritage armors)
Maybe teasing 9.2.
I don’t think they’ll announce anything exciting for WoW. Yes, I’m bitter.
Every city and location in WoW updated with more NPCs, more unique dialogues, secret treasures, new achievements and challenges. New housing system, loot overhaul, dozens of new recipes for every profession, and a new realm of the Shadowlands along with a new covenant, new dungeon, and new battleground.
lol jk there will be an Oribos raid and like a new questline about Anduin’s feelings
Lots of mobile garbage talk. Nothing I’ll want or care about.