Hey Sondre, I was waiting for some of the more experienced builders to weigh in here with the technical explanations of why the pinned bridge has won out over the tailpiece on flattops. I won't get into the theory since I've only finished build #7, but I did just finish a flattop with a tailpiece that works great. Here's the thread,
viewtopic.php?f=10101&t=22463.
I think there is a valid place for them with a lightly braced top. There were a lot of them built in the 20's and 30's, and a lot of them weren't very good, but I think it was mainly that they were very low end guitars anyway. Some of the higher end 12 strings from that era were great, making use of the tailpiece to transfer the higher tensions to the tailblock, and Todd Cambio at Fraulini guitars is building some great tailpiece models, check out his website.
So I'm definitely going to be exploring this area further, jump on in and let me know what you find out.
Joe