"Perfect is the enemy of good."
My goal is to finish the V5 documentation, not rewrite the docs. Using mkdocs will speed that process because markdown is so much quicker to write in than raw HTML. If it also gives the docs a nice new facelift for nearly free, so much the better.
I do agree that the User's and Customization guides are getting pretty long and cumbersome, but they work. Overall, the docs are "good enough." If someone wants to completely reorganize them, I'm open to the idea, but it won't be me! I'd rather go sailing. :-)