What about a 100MP with PTZ, IR, lens defogger, window wiper? I'm not sure how much better compression tech will get for video either. Phase One already has a 100MP digital camera available. An uncompressed tiff image from that is just over 800MB in size, at JPG 90% it still makes a file over 10MB. Figure 25% for fun though - the image will be pretty awful with that much compression, each frame would then still be over 2MB. So if you have more than a few cameras (we all do right?

) then you are going to get some wretched frame rates. Granted - that is all future talk. Even though a 100MP image sensor is available, I doubt we would even see one in a run of the mill security camera. 12MP is commonly out though.
I see it from the perspective of running a sign company. We were already choking a gigabit network with just 6 users pulling large files from the SAN so I recently added a 10GB Brocade switch and 10GB fiber to the desktops. It flies now. I see the same thing in a lot of other scenarios as well with the heavy streaming everyone is doing now and everyone wants higher and higher quality.
My new 4K Dahua NVR even has its limits (its a 16 channel) if I were to connect 16 4K cameras to it and tried to keep the quality on all up high I'd need to get an enterprise class switch with a beefy fabric to handle to bandwidth needed. Better cable tech is not just about power either....
A lot of factors come into play like connectors, heat aggregating in cable bundles, distance and speeds, etc. The other bummer with POE is that it is DC power instead of AC. DC is terrible for loss on distance. Hence the reason we used Tesla's AC power system instead of Edison's DC power system for long distance power transmission.
And no - I do not put a ton of weight into Beldens marketing. They do make top notch cable but its too pricey for me... I get 1000' rolls of Ice Primal Cat6 wholesale for just over $100. I've just learned over the years that science fiction very often becomes science fact and technology moves rapidly. Future proofing is not for everyone but its also not a waste of money either if it makes sense (not going to bother with something nice you will leave at a rented apartment for example).