Seven lines, and the lines could be longer if necessary. The Finnish Possession, Pirate Ship, Noble Brigand and Young Witch each have nine lines (Young Witch even has a "_____________" in addition to that), so it's definitely possible to fit more text there.
And in the same expansion, we have Urchin and Hermit (cards that add a lot of complexity to the kingdom on their own), Procession and Band of Misfits (cards with extremely complicated interactions with other cards), and a lot of stuff that modify a lot of the basic game mechanics (Shelters, Knights, Ruins, Rats, etc). It's not exactly a casual-friendly expansion at all, so there's little point in making Rebuild casual-friendlier.
I've already talked about Possession.
Pirate Ship and Noble Brigand (and to a lesser extent Saboteur, etc.) get a pass because Attacks have to ramp up in complexity faster than other cards. There are really only 4 ways to do an attack, yet about 1 out of every 6 Kingdom cards is an Attack card in order to keep the interaction level of the game as high as it is. That means that in order to keep making unique-seeming Attacks, new Attacks have to get more complex. On top of that, wording even the simplest trashing attacks takes a bunch of text. So there's that.
Young Witch, Urchin, and Hermit have some of their text under the line. That matters. Setup text especially is not something that players have to worry about during the game.
Concerning Procession and Band of Misfits: I do not care how many complex interactions a card has. Or rather, I do care, but if a card can be worded simply and yet have lots of strategic combos with other cards, that's a huge mark in its favor.
And it's not just the raw amount of text. For some reason the whole "Name a card and then dig for a Victory card that ISN'T the named card" throws some people. I couldn't tell you why.