Between the Destiny 2 bundle in September, and the high likelihood of Call of Duty: WWII and Star Wars: Battlefront 2 bundles for the holidays, I don't think it'll be hard for PS4 to maintain momentum this year.
Yeah, they've certainly got momentum on their side all year. And that's why I don't see aggressive permanent price drops happening for Holiday 2017. If Sony does drop, it'll be for the Slim $249 with a game. PS4 Pro could stay at $399 or drop slightly to $349, bundled games in either instance. MS pricing X1X at $499 gives Sony a lot of flexibility (if Sony even wishes to directly counter at all).
Worldwide, has Sony ever had so many bundling possibilities?
PS4 Slim + Starwars Battlefront 2
PS4 Slim + Call of Duty WWII
PS4 Slim + FIFA 2018
PS4 Slim + Knack II + Crash Bandicoot N.Sane Trilogy
PS4 Slim + Gran Turismo Sport + Wipeout Omega
PS4 Pro + Destiny 2
PS4 Pro + Horizon Zero Dawn(w/ The Frozen Wilds) + Uncharted 4(w/ The Lost Legacy)
PS4 Pro + Gravity Rush 1&2 + Nier:Automata Yass Queen Ultimate Crossover Bundle