I have subscribed to the forum and posting an answer to this thread. Something happened to google groups, preventing me from posting
I have to admit that my postings might be inaccurate as a human being, but rest assured that such cases are completely unintentional.
On that thread I had observed that policy.EvalSimple was not present in /etc/qubes-rpc by using strace and by tailing /var/log/qubes/guid..log
After having time to look at the source, it appeared that the qubes-qrexec-policy-daemon service was disabled.
After enabling the service the policy.EvalSimple socket began to exist.
And no need to downgrade at all, though I tested it using the testing repositories latest update as of today, i expect the regular repo to behave in the same manner.