Well 3 of its packs are in steam's top 10 sellers. Dying light is at the top seller with currently 270k concurrent players. If you count all the packs together, it wouldn't be a stretch to say there's about 500k concurrent players in just preorders at the moment. Once all the paid streamers start playing and advertising this game, it will sell even more during the head start, and once the f2p flood gates open all the casuals and hype bandwagoners will join as well. It might hit 1 million concurrent players on the 11th but maybe being too optimistic here. Honestly I hope it won't so I can actually play the game instead of being trapped in queue.