Ok, so now that I've had some time to digest all the info, I wanna say some things. Maybe it's because I analyze data for a living, or maybe I'm just reading too much into it, idk. Either way, I just want this off my mind:
Firstly if you're heavily disappointed that AC didn't make an E3 showing: I sympathize, but tbh...

Nintendo emphasized repeatedly that this would be showing for NEW and UPCOMING games in 2021. "But what about Smash and Hyrule Warriors??!?" you say. Those are1st party paid DLC, and will be advertised whenever there's a chance. So unless you wanna start paying for AC DLC ala Pocket Camp leaf tickets, then uh...yeah.
Secondly, no, Nintendo has not abandoned AC or fan of the series. AC is big enough now that it gets its own Directs, like Pokemon and Smash. It's the second most sold game on the Switch for all of 2020 and most of 2021. Nintendo knows that it can take the spotlight off for a bit and showcase other games.
Thirdly, in every game in the series, even back from Gamecube through the 'universal code' system, Nintendo has supported each AC game for literally years, especially with item downloads. New Leaf was the first game where we got not only new items but gameplay modes. But that came four years after the NLs release. I'm only guessing, and I'm not telling people to be patient or feel some sort of way, but I don't think NH will be any different. Nintendo all the way back a few months ago announced dlc items for AC up until midsummer. For me, that was the biggest red flag that they weren't gonna show anything for AC for a good long minute.
Analytically speaking, and this is just me talking personally: do not expect to hear anything about AC until August, at best. And please understand me: I'm NOT saying I'm right, just that this is what it looks like to me: There will be a 2.0 update but it won't be anytime soon. Anything we get this year, will be for items, mini-updates, or for events that we've already experienced.
For real, the only thing I'm hoping for in the short term is the villager bug to be fixed so my villagers can start revisiting the museum.