I doubt there's going to be too many side activities and if that's the case I'm fine with it.
Activities based on existing mechanics (shooting, melee, driving, spider-bot assault course etc,) are what I'm used to seeing in games and are more than enough for me but, obviously, how they're implemented will decided how fun they are and how much time I'll spend on them.
For example, a shooting range doesn't sound that exciting, but I've played games that include them and had fun. Resident Evil 4, Evil Within 2 spring to mind. The latter had shooting that incorporated some kind of puzzle element. I can see that happening in a futuristic arcade, a neon lights/tetris style type thing, you know? In fact, given it's sci-fi, there's no reason a 'shooting range' has to be some static activity, blasting card board cut outs.
I've also played games where I wished I could try before I buy. Sure, you can always quickload, but in a game like this you might spend 30mins after leaving the shop before getting into combat and testing it out.
Motivation plays a part in the satisfaction too. Xp, money and, in the case of CP, street Cred? Special items/clothes? They have options.
Still, the side activities aren't that big a deal to me. I really enjoyed Gwent but, in all the ways that truly count, I'd have enjoyed TW3 just the same without it.