Well first I don't expect anything to be announced for anything until right before it opens.
My guess is we'll see at minimum one hotel and Fantastic Worlds built by 2023 or 2024. I think more likely it'll be two or more hotels, since they don't necessarily need to open them at the same time as Fantastic Worlds. It's possible they have an "open a hotel every year" mindset, so we could see something open in 2021 and/or 2022 (after Surfside and Endless Summer). A City Walk 2.0 would likely either come on, before, or shortly after FW.
By the time Fantastic Worlds opens (around 2023), I'm betting we'll have a good idea for what they have up their sleeve for phase 2 of the property. There's a big "if" though... If the economy is in a slump, or if Comcast specifically is in a slump, or if FW doesn't do as well as they hope, I think that'll slow things down significantly.
But consider the precedence of Universal Orlando right now: we constantly have seen big expansions (hotels, large lands, water park, theme park). Why anyone would think this would stop around 2023 (aside from external forces) is beyond me.