where are you getting the idea that source 2 will have advanced physics? it's just a video game engine, any physics features will have to be very rudimentary to work in real time. certainly nothing that would make jizz hitting a face look even remotely real. decent fluid simulation needs to be pre-baked (possibly hours per frame) and that's not something you implement in your real time video game engine.
for these animations to have advanced cloth and fluid sims the animators need to abandon sfm in favor of real software. sfm is just a rudimentary tool for making tf2 machinima, if you need fluid sim you will have to look elsewhere (maya, max, or even just blender). sfm is basically a toy and will never have the features of a real 3d suite, source 2 or no source 2.