An ultimate evidence for quantum entanglement would be a quantum computer that fulfills huge promises.
So far, I do not exclude the possibility that apparent symmetry and EPR can be alternatively explained just as consequences of inappropriate mathematics, cf.
http://home.arcor.de/eckard.blumschein /M283.html .
An analysis in terms of cosine transform shows that h_bar is not necessarily related to the imaginary unit.
John v. Neumann admitted in 1935 having lost his belief in Hilbert space. Already in 1932, Hermann Weyl did not have an explanation for PCT symmetries. Who is interested in more details and more recent arguments?