https://www.youtube.com/watch?v=qZaVTM0ypO0So the frame is finally up. Let's try to analyze what new information we have. In the tweet, she said there will be a "luxurious guest" (豪華ゲスト) which usually implies someone that's a big deal from outside the company.
In the description of the video she says something among the lines "they let me do something that I have been wanting to do" (やりたい事を やらせて いただきました). I had a look at her official stuff she wants to do list in the description of her free chat but none of them really fit anything you could do as a stream project.
She also says there will not only be a major announcement, but a "super super super major announcement" (超超超重大告知) and I feel like she usually isn't the type to exaggerate about nothing. Looking at her list, the only thing that come to mind would be "Sololive", "collabo cafe" or "do work as a voice actress", but I'm not entirely sure if either of them fit the description of "super super super major", except maybe the Sololive, but everyone kind of already knows that has been in the work for a while even if not officially announced.
And finally, in a subsequent tweet, she says this project is something so outrageous that you would never imagine when looking at the cute thumbnail (想像もつかないようなとんでもない企画). To be honest, I got nothing, I still have absolutely no idea what it could be but I'm very excited about it.