I doubt 2018 will be up against 2017, the PS4 is starting to get old and market saturation is slowly starting to set in, too. There's also not much Sony can do anymore with the price; a 50$ price cut is probably incoming this year but this will be probably the lowest the console will sell outside of promos
I do think however that while the PS4 as a whole won't be up, the PS4 Pro sales will be higher than 2017, slowly drawing closer to the base model's sales
Historically whenever Sony have dropped the price, sales have always gone up. So If you have other proof as to why a price cut would cause sales to drop instead, I'd love to read that link to see how that happened.