Does anyone know what the thinking behind the ability to sustain the crew for several days is? Is this just a step on the way to being able to sustain a crew for lunar/Mars flights or does it have any immediate utility?
For the past few years, manned missions to the ISS take only 6 hours in ascent, all the rendez-vous maneuvering is being done in the duration of 4 orbits.
It used to take a few days, though. However, the crews take a pre-flight enema [0] and go through a diet to avoid having to go #2. There's a story that the Soyuz toilet has been used only once in ISS missions after a Cosmonaut had been eating prunes prior to departure back to earth [sorry, can't find a link].
So for orbital operations to/from the ISS, there's not much use for a space toilet. So little, that I wouldn't be surprised if there's no toilet at all and the fallback plan is to soil your pants, as crude as it sounds.
[0] http://gizmodo.com/5245218/the-trouble-with-space-toilets
When Hadfield went up, they were still using the older long procedure.
For long-duration missions, the PICA-X heat shield has plenty of margin for a direct entry from a lunar or Mars mission. Dragon systems seem happy enough so far loitering at the ISS for an extended duration. However, the Dragon itself is still pretty darn small and may require an additional logistics/living module, which it could dock with like Apollo did the LM. Such a thing wouldn't be too hard for SpaceX to make up.