I debated this which would have meant an re-design of the base, but two things convinced me to keep with the traditional design: 1) It would have meant buying more lumber which is a bit of a pain for me where I'm located and 2) the adjustable bench slave (I have yet to build) is quite useful for supporting not only long boards, but also drawers or anything you want to clamp in the tail vise.
I actually went through several other iterations and re-designs relating to the vises, but in the end stuck with the original.
Glad I did. The more I use this bench, the more I like it.
For anyone considering the build, I might rethink the tool tray, or at least some type of cover for it. Also, a little trap door clean out.