WhatsApp uses the same encryption as Signal and chat screening won't be exclusive to WhatsApp anyway, so whatever WhatsApp will need to implement to comply, Signal will have to follow.
End to end encrypted, I think chat control is all about client-side scanning so the app being open source is a big deal and would prevent client-side scanning because even if they build in client-side scanning, it's open source and people can remove it.
Signal is pretty control freak-y, so would not be surprised if they can somehow prohibit third-party modifications entirely. That would be out-of-character for them, though, so doubt they would actually go through with this.
Still, if that went through, I'd discount all the centralized solutions.