I just tried vc-p4 and it works in principle, but in ediff mode the buffer with the old version has a text: at the beginning of every line. This is because p4 is called with the -s option to prefix its output. probably it should be removed during parsing the p4 output?? Is vc-p4 still maintained?
P.S. This is how I use the package:
(load-library "p4") (require 'vc-p4) (setq p4-do-find-file nil)