Ok, we can discuss whether the changes are significant but the fact that changes are required at all is the main problem.
You don't get new features without change of some sort...
Sure. But wouldn't it be better to keep the number of places where changes are necessary to an absolute minimum?
"absolute minimum" is not a good terminlogy for technical discussion.
However, even if we change something for multihoming, it does not mean we must change API nor source code.
That is, we should use the current IPv6 API for applications, if any :-), already running over IPv6 even if a host is multihomed.
And, it is being done with 8+8 addressing, as is described in:
http://www.ietf.org/internet-drafts/draft-ohta-multi6-8plus8-00.txt
Masataka Ohta