Exactly this. We used to call them Adventure Packs back in the old EQ and EQ2 (before it was F2P) days. 10 bucks and you basically got a small zone with a dungeon. Some nice gear that was relevant yet only obtainable in the zone / dungeon and some other silly vanity stuff. They usually kept you busy for a month or two, untill either the next one or the next expansion came out. The nice thing was they wern't mandatory to have. This Adventure Pack is. By increasing the level by 5 they are making a requirement for you to buy an Adventure Pack.
Now granted we are most likely (read hopfully at least) going to get playable Cathars; but unless this planet is as big as Hoth, Voss and Corellia combined, and the amount of exp required to get from 50 to 55 is the same amount that is required to get from 20 - 50 I see people burning throught this in a few days.
Please EA call this what it is. You want to make an actual expansion you're going to need to add a bit more than has been mentnioned and/or previously promised.
Do you know that a lot of people burned through MOP in a day? The expansions aren't targeted towards those people. They are targeted to the people who play, enjoy it but have LIVES! Sure, in a couple of weeks to a month, the leveling content will probably be burned through. However, that's what a half-size expansion like this one will do. MOP, a full expansion, double the amount of time.
When it comes to new classes, I really don't understand this argument. Adding new classes would take forever with the way SWTOR does it. And now 5 new levels on top of it? Forget it. WoW can add new classes because not much is required for missions in their game. We're not getting new classes and, honestly, I'm okay with that.
When it comes to the planet size, I'd bet it has about ten times the content as Voss or Corellia. With the XP increases, that will be needed. And with all the bonus quests they put in (you know, ability to outlevel the planet), we will have a large amount of content.
As for no extended class stories, we knew this was going to happen. The story couldn't go on forever and they even said before (we all know how much we love to throw that around) that it was going to come together into one story. They made the connection to the Avengers but take that as you will. All chapters will probably deal with an overall faction story which I'm pretty excited about since now they can really escalate the war (which people have been complaining about). I think it's a good, solid expansion and look forward to the release.