For what it's worth, I'm glad NeoGAF is still a place you can go to see opinions from all over the place. While there are some borderline fringe hot takes here, it still makes the discussions far more natural as you have a variety of takes. Definitely prefer this compared to the other places, especially as the moderators here have been doing a good job keeping thread shitters under control.
As far as the Witcher 4 announcement goes - I think with how the games went, especially 3, they pretty much showed that Ciri would likely be the next candidate to carry the torch in the series if they were to continue. As far as we knew (aside from rumors), Witcher 3 was going to be the last game. I understand that there are a lot of fans of Geralt and they want to see his journey continue, but I believe a lot of fans also feel that Ciri would be a natural choice too. Whether they pull a Metal Gear Solid like they did with Snake/Raiden (whether you liked it or not lol), who knows. I do recall the voice actor for Geralt was doing something with a project, so I would assume we'll probably see him return in some fashion in The Witcher 4. Whether they split roles or he is just a side character/NPC I have no idea. It's way too early to tell at this point, I just hope this game isn't like 3+ years away.
Regarding her design, I'll probably need to visit The Witcher 3 again. However, I think she looks very close to her original design. While I'm sure most of us would prefer her younger design that we remember, her most recent design in the trailer looks fine to me. Slight deviations/variations were apparent for sure, but I'm thinking we'll see a detailed look at what has happened to her (I hope so!) since The Witcher 3. I'm assuming she's been through a lot of shit both physically and emotionally, especially a time lapse. I assume she is probably 30+ years old at this point, if not older.
We also have to remember this was rendered in UE5 for the cinematic. These enable far more facial expressions than we'll likely get or are used to getting from Ciri, so it definitely gives her a lot more facial expressions we haven't seen. Like other users have mentioned, we'll have to see how her in-game model will look like. I'm assuming they will be different than what we see on this trailer versus what we get in the game. Might not be a huge difference, but it'll still be noticeable.
As far as why/how she is now a Witcher, we won't know anytime soon (aside from the recent interview that came out saying she went through the trials) - we'll have to wait till the game expands on the lore or they do additional minor PR/Developer Interviews. Given what we know of Ciri and how powerful she was, I wouldn't doubt it allowed her body to live through the trials. Unfortunately, I do see her power getting nerfed or restricted once the game comes out. Would be cool to do some crazy stuff with her, but I'm figuring she'll be restricted in some way and I'm sure her lore/story will likely center around it.