> If it's to be believed, IPv6 transition is quite far from "smooth".
Yes but it would have been much worse (read: impossible) if IPv6 deployment ever required substantial changes to IPv4.
This is an interesting article. Except they are wrong when they pretend it is easy to break backward-compatibility with Ethernet or TCP. It is not easy but only "less impossible" than breaking IPv4 backward compatibility.
Note: the focus of the article is obviously neither on Ethernet nor on TCP.