In America yeah it wouldn't hurt them that much I think, but in other markets where Xbox does poorly it'd remove the negatives of buying a non popular system.Yeah, it may cause them to make a direct loss but indirectly or in the long run I believe it would be positive for them, not to mention the good-will and positivity it would create.
The cat is out of the bag and I doubt Sony can just sit on their hands and do nothing, but as you say they need to be proactive and make sure they can start crossplay discussions while they still have negotiation power.
Thinking of a future with crossplay though, it could be interesting. Right now it's just 3 consoles but I could see it quickly becoming PC 2.0 with various companies producing their own systems. On the positive side it'd push Sony to make even more exclusives.
Sony has amazing exclusives, as long as they keep that up then playstation will remain this popular. All they need to do is match Xbox on price. I doubt it'd come to a PC 2.0 type of thing, but it may become close. However if that does happen, and Sony doesn't want any part of it, I think that would be bad for Sony, not good.
Not many people would want to miss out on the connect console ecosystem, I know I wouldn't. I'd only ever play exclusives on playstation. If Sony stay on the ball and allow crossplay etc. then I don't see myself ever moving to xbox or elsewhere for multiplats/ online games. As it is, I'm considering switching to xbox as my main console and just have a PS on the side for the occasional exclusives next gen, especially if Xbox continue to progress with this.