I am a returning player/subcriber, and I am trying out some of the new character classes. One thing that bothers me a lot, is that on these new characters I virtually have to SKIP half of the at-level content due to most people not having one adventure pack or another. I think it would be advantageous to offer a subscription-only server that caters to like-minded individuals, that don't want to have to either drop party members, buy a silly pass, or skip content entirely (at-level, you can always solo it later, but I prefer to play in groups.)
In addition, this idea of a subscription-only server got me thinking about something that Everquest had (and may still have) back when I still played it - a "Premium" server. You could pay a little more each month to have access to a server that had daily GM-hosted events, better loot drops, and an across-the-board xp bonus. They would also allow you to transfer, free of charge, X number of characters to and from this server every 30 days.
I don't know how much of market there is for something like this, with the general populace, but I certainly wouldn't mind ponying up a little extra cash for a perks-laden premium server, OR just rolling up a character on a vanilla subscription-only server using the VIP access I currently pay for.