I know a lot of people in this thread are all "CCN ololol", but I think it's actually an interesting thought experiment to think about whether Sony can continue its momentum. Just because Sony is in the lead right now, doesn't mean they're going to maintain that lead next gen; the leader has flipped in every gen so far. Sony was the leader in the PS2 era, then it was the Xbox 360, then the PS4, and honestly now the Switch is taking off like a rocket. Most customers don't have huge brand loyalty to one box over another, especially when most of the market is playing multiplatform games like Call of Duty and Assassin's Creed.
A big reason why the PS4 succeeded at the beginning of the gen was because the alternative (Microsoft) was completely tone deaf and not focused on gamers. Microsoft today is very different from Microsoft 7 years ago, and I'm convinced they're going to bring the heat next gen. They proved they can make a fantastic console with the Xbox One X, they've been ahead of the curve on backwards compatibility and cross-play and subscription gaming, and they're definitely going to be better than Sony at streaming given their cloud infrastructure. I think it would be silly to write off Xbox just because Sony is currently in the lead.
Another thing to mention is that while Sony has a lock on epic, narrative-driven exclusives (God of War, The Last of Us, etc.), Microsoft is much stronger in the multiplayer arena (Halo, Gears of War, Forza). If they can build out their stable with a handful of truly compelling multiplayer offerings (Sea of Thieves, Bleeding Edge, etc.) then the massive chunk of the market that plays multiplayer games could be swayed towards the Xbox.