While this would be great, it doesn't seem very likely. It would be clunky doing the transitions between the players turns without anyone seeing the others hand, and also the entire Gwent game will be built around building up your account. Would your friend play with the same cards, achievments, friendslist etc. that you do or would they have a separate account?
And as the game is f2p there are gonna be very few people who couldn't just play on separate computers, so they would be putting their time into a feature very few people would use. Local coop is rare enough on pc in games where it works very well, and since it would be so clunky in this game it would be very unexpected if they put it in.
Not saying it wouldn't be cool (though I personally wouldn't use it it doesn't hurt to have more features), but I don't think CDPR will do it.