I would like to see a Ciri cameo in Cyberpunk, but it should be done ambigious.
I wouldn't want to see Witcher 3 Ciri arriving out of nowhere using magic.
Make it vague, make it interpretable.
Don't let her appear in her Witcher 3 clothes with a sword on her back.
Change her appearance, so she is still recognizable, but doesn't look like we know her from Witcher 3.
A different haistyle, different hair colour, different clothes, a slighty different name.
Let us talk to her but avoid anything that may break the mood or the lore of Cyberpunk.
Don't let her say that she is from "another world", but from a "place far away".
Don't let her say that she can" teleport", but that she has just "special abilities".
Maybe we could get a small mission with her. But again, keep it vague.
She is fleeing, the Wild Hunt is after her. But don't mention the Wild Hunt or even show them. Just show some shadows. Let our protagonist think some random (Cyberpunk) thugs chase some random girl. Maybe let us hear a voice similar to Eredin out of these shadows, but without our protagonist knowing whose voice we hear.
Give us a small mission in which we help her. Something banal, like helping her to find a shelter or food because she didn't eat for days.
If done right everybody could interpret it in a way how it pleases him/her.
The people who don't like mixing the universes or introducing magic or even don't know who Ciri is, would just see some random young woman in her.
Others would get a nice cameo from a important and likeable character.