I can see that. However, skylake would require a special chipset for TB3. I can't see Apple putting in a chip set, then removing it in a Kabylake update six months later.
"Special chipset" is just an Alpine Ridge TB3 controller chip (which includes USB 3.1) same as Dell and everybody else are using. The current Macs all use a discrete TB2 controller anyway.
Kabylake (certainly the mobile versions) will, presumably, only support 2 TB3/USB-C ports anyway, so if they were going to go with 4 ports (as per the rumors) they'd need a discrete controller as well, anyway.
A "compromise" would be to launch a Skylake rMBP with 2 x TB3 (USB-C sockets) and 2 x USB 3 (regular USB sockets) - assuming that Jony hasn't made the things too thin to fit a regular USB socket in - and go to 4xTB3 a year or so down the line (still with only 1 discrete controller). 2xTB3/USB-C with 3.1gen2 and 2x borked USB-C with 3.1gen1 (as per Macbook) would be confusing (and would still need a USB-C socket controller).
What probably
will wait for Kaby Lake is any rumored 14" MacBook or 13" rMBP replacement which, I'd guess, will just have 2 ports.
I have an 11" Macbook air, and I use Ethernet and VGA every day at work. We have projectors in every conference room with VGA cables ready for the laptops. I have a direct ethernet connection to the PC under my desk for remote desktop and access to sensitive files that we cannot put on the cloud.
...so, presumably, since the Air has neither ethernet nor VGA, you've learned to stop worrying and love dongles? With USB-C you can reasonably hope for more products like thus:
https://www.amazon.com/Dell-Adapter-Type-Ethernet-470-ABQN/dp/B012DT6KW2 - at cheaper prices than Thunderbolt docks have been.
USB-C is going to be a pain at first, but long term it should become a benefit
if USB-C becomes the standard connection of choice across Mac and PC. If Apple comes out with USB-C only laptops it could help push this (the PC world hasn't even weaned itself off PS/2 keyboard sockets yet).