It seems pretty simple to me. Do you have a 4K TV or in the market for one? Here's a product that can take advantage of it. If you don't have a 4K TV and not interested? Don't bother. Outside of resolution there would be no quality or performance difference. That's pretty straight forward. It would be just another SKU.
Now if there is a performance difference with PSVR, then that it is a whole different story and brings quite a bit of marketing problems.
You have to explain to a fraction of 36 million+ current PS4 owners who are in the market for PSVR that there will be a quality difference with a new SKU. Even though most of those people have never tried VR in the first place an wouldn't how much better or worse the experience be with their current hardware. Do you have to pay another $400-$500 for the new PS4 on top of the $400-$500 you've already committed to PSVR? If Sony is this quick to update the PS4, will their be another expensive headset in a couple years that takes better advantage of this new PS4?
If this is just an updated PS4 that can play the same games in the same quality with the only difference being 4K resolution which the appropriate display is required, then this is fine. Anything more than that, especially with PSVR, it would be a big mistake.
I don't think Sony are going to release a new console, which is much more powerful (3-4 times faster than a PS4), possibly cannibalizing PSVR sales and alienating it's existing userbase, just so 4k tv owners can play the same games at 4k. That doesn't make any sense.
I think you may be right as in this is not about 4k, this is about VR.
Let's get deeply hypothetical here.
Let's suppose AMD has Polaris ready for this holiday season and it is all that AMD promised. Cheap, powerful, low consumption. So Microsoft (and/or even Nintendo) could have a 6tflop+ machine in stores for 450$ before the end of the year. If one or both of this companies partnered with Oculus for example, they could have a real next gen VR experience by the end of the year to compete with PSVR.
By real next gen I mean a machine capable of runing Battlefield 5, Forza 6, GTA V... any current gen game in VR. PSVR would look like Fisher Price VR in comparison, and it wouldn't be all that much cheaper.
In this scenario, it makes sense for Sony to release a backwards compatible PS4.5, so they have a product for everybody. Sony would be basically forced to release PS4.5 this year if they don't want to miss the VR train.
If this is the case, then everything makes sense and I understand Sony is forced to do this, and this doesn't necessarily mean that consoles are going the iterative way. I would be ok with it, but they are going to have a hard time explaining this to their millions of users that just bought a PS4 maybe in anticipation of VR gaming.