Attached patch takes care of making sure that /dev/.keep and /proc.keep are created very early in the stage making process...they are no longer added by baselayout on FreeBSD systems as both file systems are not writable and once they are bin mounted in emerging baselayout with the buil/bootstrap USE would have failed...
Created attachment 100913 [details, diff] Patch to fix the issue
This is now in SVN.
Fixed in 2.0.1