You can already tell if someone is on PC or console. Click/Highlight any person and Examine them. If they play on console, it will show your PSN ID name under your Avatar's picture. If there is no ID there, they are on PC.

That being said, you can get a keyboard that works just fine on PS4 for less than $10. "Being on console" is not a good reason to not communicate in a game that requires it for high tier content.