From my look in the Vim sources, it would be tons of work to truly make it use pcre internally.

But I think it wouldn't be hard to do a plugin that translates a pcre into a Vim regex, allowing you to search or replace using pcres.

My code though is not integrated with Vim, it takes a free floating regex and converts it. I used it to convert all the regexes in Vim syntax files and build a syntax highlighter. It was a silly project, just for fun.