Separation of tickets and VCS: that has been a bit of a stickler in the development of libfossil (http://fossil.wanderinghorse.net/r/libfossil). In fossil the ticket system is married to a custom mini-script engine called TH1. In libfossil we want to avoid any specific script binding. That's turning out to be quite difficult, as Fossil's ticket system is built from the bottom up on top of TH1 (which is not a very flexible language).