I think you guys underestimate the importance of a club feeling.
A subscription based game is more than the sum of its parts. It is belonging to a club mentality.
The effort of taking a subscription is really making a statement of belonging to that club.
Very important for an MMORPG.
I read it a few months back when a stock analist came up with this theory.
He answered a question why WOW remained with 10 million subscriptions (and all that money) while new games failed to keep players in.
Belonging to a club with a paid membership is an extra motivator that free to play games don't have. (of course it is not the ONLY reason, but it explains an extra motivation to keep "playing" even if you hardly log in).
My guess is that Blizzard wants this feeling to spread all over their games through BattleNet.
That's why I think they will go with a BattleNet subscription fee for all their games combined and all services included: WOW, D3, SC2, Blizzard All Stars and of course Titan.
The underlined scenario is far more possible than a free to play WOW in 5 years time. Of course a Blizzard club fee of 15 Euros is a nice replacement for their current system.