If the PS5 really is due out next year (which is highly likely), then I'd be inclined to say we won't see anything, especially in light of similar things on the PS3. The PS3 Super Slim had no real impact on PS3 sales, so I don't see Sony coming out with a PS4/Pro Super Slim unless it would make the hardware more profitable over the remainder of the PS4's lifespan. And we've never seen a price cut this late in a system's life, with the latest being in Year 5; the PS3 got a $50 price cut in Sept. 2012, and while it did have a stimulative effect, it was short-lived. As with a hypothetical Super Slim, I don't see Sony issuing a price cut unless they think it'll make the PS4 more profitable over the remainder of its life, because the benefits to sales volume provided by late-life price drops aren't that great.
they could've reached over 90m PS3s easily with a cut to $200 in September 2012 (for the 160gb)
They should not miss their chance to get more hardware and therefore more PSN accounts and software sales before PS4 runs out of life. Gotta get it to the mass market price PS3 never reached. There's no cell to keep it expensive this time. They will still profit at $200 and it will get them huge sales. Bundle it with a big software title like GoW, Spidey, Days Gone, etc.
If they don't lower price on both it will be a weird situation of PS4 Pro being the same price as PS5 and PS4 base being just $100 cheaper. Would kill late sales of PS4 (that's one of the big reasons PS3 got cut off was because its price was still too high).
Both Slim and Pro will have price cuts by the time the PS5 arrives; I doubt they are going to let the PS4 just die off like that.
But that said I disagree with the idea that they will get more PSN accounts (I assume you mean subscribers for online). At $200 you are most likely hitting an audience that doesn't have the money for a continual subscription, or are getting a PS4 as an additional device to what they ow, meaning they dont need the subscription most likely.
i dont think there is a guarantee that get more money from a lower PS4 than what they have it priced at now.
A price cut i time for Days Gone or TloU2 will definitely help with mass market appeal, but I am sure it is done in time for PS5s arrival at least, creating various tiers for users to jump into.