Just the opposite here. Right now my 2012 MBP is sitting on my desk. Plugged in to it are Ethernet, the charger and a USB3 cable connected to Time Machine #2. For me connectivity is very important.
I have a similar setup. I plan on leaving my MBP on my desk, hooked up as you described, and the new Macbook is what will be coming along with me when I leave my office. I can always log into the MBP remotely, should I need something with more power, which would be rare.
I really don't see using my 15" rMBP on my desk and using the new Macbook when on the go as any different than using my computer tower on my desk and my (more bulky) laptop when on the go, like many of us did 10-15 years ago.