I just bought a 2015 WRX, and when filling it up today the fuel filler door would not open. I had to use a credit card to pry the door open. Searching the Subaru Technical Information website I found TSB 09-57-14, issued June 11, 2014, which describes a fix for this problem. It applies to all WRX and STI models made before April 23, 2014, with VINs earlier than 808794. It calls for new part number 51469VA000. It is a revised spring and new ring clip that should make the door pop open when the release lever is pulled. The TSB says it takes .5 hours and is covered under warranty.
I don't know if my dealer has this yet since it is so new. However, it is an annoyance worth fixing.
Love the car.