as a player, I'm not really sure what would be gained from a sequel to csgo. any big change to the mechanics would just piss everyone off, and smaller changes can just be done as updates to the existing game. csgo was only ~$20 when it launched, and it's free now, so I don't think there's much financial upside to selling a newer cs title. they already make plenty of money off skins.

the only thing I see that they could really change in a new title would be the graphics, but I don't think that's much of a selling point to the audience. cs players care more about getting >100fps on their potato computer than pretty graphics.