Well, this is something that Bethesda’s actual games need- they would probably launch in a better state than they do right now. Bethesda have announced that they will be holding beta tests for all upcoming Fallout 4 DLC (the first wave of which was just announced today).
The beta tests will be closed betas, and they will be run on all three versions of the game. Registration for these tests is open right now on Bethesda.net. A Bethesda account is necessary to sign up for these tests, and Bethesda will be selecting testers from the pool of applicants in the coming weeks.
The beta test in each of these cases will be the full, final version of the add on, complete with Achievements/Trophies- and if you are selected to participate in the beta test for an add on, you won’t have to buy it once it releases.
So, not only do you get to play the add ons early, you get to play them for free. I’m pretty much on board with anything like this.