Quantum Mechanics without wavefunction

During my studies I was fortunate enough to write a short review on density functional theory, specifically reduction of computational burden in computing many electron integrals [pdf]. What strikes me in that short literature review a quote that is attributed to van Vleck about the legitimacy of wave function in standard quantum mechanics: ".. wave function has no legitimate scientific concept as pointed out by Van Vleck for many electrons (more than 10 electrons)..." according to Nobel lecture given by Walter Kohn, so the concept of density functionals in solving quantum mechanical problems. In similar lines, recently Israeli-american scientists has formulated the non-relativistic quantum mechanics without the need of wave function or density functions : Quantum states are represented as ensembles of real-valued quantum trajectories, obtained by extremizing an action and satisfying energy conservation [link] I think interpretation of this new results might be quite interesting, worth to think about it.