This base theme is a great start, and I think it will speed up the creation of custom themes for clients.
One thing I wonder: Do we want it to be useable out of the box? Like with sidebars in their proper place and the headings set to relative sizes?
The Stark theme in core is a bit like that.
No worries if we just want to always take care of layout in the subthemes, since most sites will be quite different in their needs, but I'm curious what others think.
Jeff