It's not an expansion, it's a DLC. They're not even close to being the same thing.
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.