The only way I see PS getting away with holding off to announce PS5 until 2020, is if they pack 2019 with first party AAA exclusives. That alone should be enough with all the third party and indy games in between, to keep people happy and busy enough that they don't really notice the lack of events. PS4 price drops would also help.
Otherwise if next year isn't that much different than this year in terms of first party exclusives, then I would assume the PSX event will be a huge 25th anniversary celebration with the full PS5 reveal. Whether it launched soon after or in early 2020, I don't think it would matter too much if PS4 is locked at $199 by then.
PS1 - ! - We must build a console that can alert our enemies.
PS2 - @- We must build a console that offers online living room gaming.
PS3 - #- We must build a console that’s powerful, social, costs and does everything.
PS4 - $- We must build a console that’s affordable, charges for services, and pumps out exclusives.
PRO -%-We must build a console that's VR ready, checkerboard upscales, and sells but a fraction of the money printer.
PS5 - ^ -We must build a console that’s a generational cross product, with RT lighting, and price hiking.
PRO -&- We must build a console that Super Res upscales and continues the cost increases.
