I think the 2.55 lockout is both good and bad.

The good: Most current players will already have the quest chain done or at least finished up to 2.0. It won't be hard to finish the questline, and it is pretty cool that it will continue to follow you all the way to 60.

The bad There are a LOT of quests at level 50. A new player who is leveling would quickly hit a wall of quests and find that they will have to grind countless quests before they can continue to level past 50. Unless they are going to change the level requirements of some of the story quests or let people continue past level 50 without completing 2.55, this will become an issue.