Jumping to new nodes is more expensive until they become more developed.
Granted. Jumping on an immature fabrication process would be costly given the potential for bad yields. The FinFET process has been struggling for a long time but it's finally becoming stable with enough good yields. We may or may not see a slim PS4 this year depending on the capacities but it will eventually arrive (if Sony decided to keep making it).
Er... you answered your own question, and ignored the post you quoted. The PS4 can benefit from the reduction - it's called the PS4K. Mark Cerny designed the original PS4 hardware around dropping manufacturing cost organically across the generation to ensure healthy hardware profits. This was a big reason for the GDD5 RAM - it's only getting cheaper. The PS4 Slim has literally no reason to exist, and Sony have zero motivation to produce it. Due to the obtuse RAM configuration and APU design of the Xbone, Microsoft have a very real motivation to re-design. You're not looking at this from a business point of view. Just because Sony can improve the PS4 design, doesn't mean its cost effective to do so, other wise we'd already be seeing yearly hardware revisions.
Okay, it seems to me you are riding on the idea that Sony would stop manufacturing the PS4 altogether. That might be a possibility but the other would be to have two SKUs available simultaneously (especially if they ended up choosing the more powerful CPU and thus raising the price of the new console to the rumored $499). In that case, a redesigned PS4 would be beneficial. RAM doesn't automatically get cheaper on its own (sometimes it goes up in price). Using a smaller node would help reduce the cost since you can print more on the same surface area and thus would need fewer modules to begin with. The supply chain would also benefit greatly from fewer variations (and more shared parts) between the two SKUs.
Sony had already announced a slightly modified design for the PS4 in June 2015 (CUH-1200) that's lighter and more power efficient, and has a mechanical eject buttons. It also featured a smaller board despite still being 28nm which suggests an improved design and a better manufacturing process.
You can see a list of difference here. So if Sony has done it already, why won't they do it again if they are going to keep the SKU alive?
