I don't think that there ever will be a "perfect" FFP, however, there is always opportunity for improvement. There are millions of things that can be done to improve a FFP, but they won't suit everybody. (eg, WP Anytime access - some people used it a lot, others hadn't used it).
My thoughts
1) Better burn rates (some of the points quoted are almost DOUBLE AA)
2) More seats available for classic award redemption (A few months ago, I looked 355 days ahead for a classic award, SYD-LHR-BUD, nothing)
3) Upgrade coupons/vouchers upon reaching milestones (I know that this might not apply to some people, but l fly Y 100% of the time, so it would effect me), or vouchers where you can upgrade to next class, Y-Y+, Y+-J, J-F and not having to wait until a few days before departure to find out, immediate confirmation.