Getting the DCs right is an important part of the playtest; i wouldn't assume that they're perfect right out of the box.
WRT the specifics of picking a lock, I mostly don't mind the idea of a rogue being able to pick just about any lock with enough time, except for how it intersects with some other rules. Sure, there are realism/verisimilitude issues with the first level master lockpick, but with flatter math, some of that's inevitable. As i see it, hard to pick locks have a couple different functions in a game: (1) they're hard to pick fast, so if there is a concern about speed, rogue ability matters; current rules handle this fine; (2) they might mean that you have to break the lock (and maybe the potions inside the chest) because you can't pick it; the rules don't enable this; (3) they might mean you need to get some other door-opener (a magic key or whathaveyou); I think the rules are fine here, because just because mundane locks have a normal max DC doesn't mean that there can't be magically or whatever sealed doors; and (4) they might mean you trigger the trap on the door when you fail to pick it (something that D&D traditionally handles separately, but that's nicely incorporated as a hazard for lockpicking in Next terminology). I am concerned about how rogues' skill mastery interacts with the Hazard rules--if failing by 10 means hitting a hazard, then no rogue will ever hit a hazard if they are trained in the skill and capable of succeeding--they'll always be within 10 of the DC. That's a problem, because that means that the fancy lock with a big trap keyed to it is not dangerous to the rogue, and I agree that that's not a good result.
As for take 20 in general, there's a tension. Sometimes we want to know "can you succeed right now?" and sometimes we want to know "can you succeed at all?" If you're trying to futz the magic runes or disable the fire trap spewing burning oil in the middle of combat, it's entirely reasonable to say that you can roll each round, with failures meaning that you fail that round (but can try again) and success meaning you succeed that round. But then it seems bizarre that when the combat is over, you get one roll and if you fail, you can't succeed until circumstances are different. But if you let re-tries out of combat, then take 20 isn't really a special rule--it's just a way of representing "I keep rolling until I get a 20." In practice, I'm not sure that take 20 really creates all that many problems, and it does solve some.
