a couple things:
according to the autoblog 1st drive review of the brz, the fa20 DOES have AVCS. that's the only source i've seen mention it so i have no idea how accurate that statement is.
it's true that subaru initially didn't want d-4s, but it's also true that initially subaru wasn't aiming for 100 hp/liter or 200hp. they were literally planning to do nothing but stick the fb20 in there as is. it was chief engineer tada-san's insistence on a 100hp/liter engine with good gas mileage which led to the development of a brand new engine with d-4s and 86x86 square bore/stroke. initially subaru had their doubts whether d-4s really had such potential while toyota had doubts that subaru would be able to build a d-4s compatible block that would meet the specifications, but they got 200hp on their first try, which removed any doubts on both sides.
this is all info from the japanese press brochure that was passed out at the debut.
http://www.ft86club.com/forums/showthread.php?t=2565