Okay, listened to the podcast, and I have to say that I heard nothing indicating 3E-style multiclassing is in. At no point did they mention anything about "taking levels in" other classes, except in the context of 3rd edition. They only mention "combining classes," which could mean anything from 2E-style to 3E-style to class training feats to something completely different. Here's a transcript of the relevant bit:
Noonan: The next question is from Sebastian Morele, who asks, "I wonder how multiclassing will be implemented in Fourth Edition? Will it be as flexible as in Third Edition?"
Mearls: That's an interesting question, because I'm not exactly sure how much I can talk about right now, but it is probably not quite as flexible in the sense that... in Third Edition, you could just take one level from every class you could care to find. We're doing away with that, mainly because there were issues with class design--that it forced you to maybe spread out class abilities a little more than you wanted to, because you always had to worry that someone could take one level in this class. So it's sort of annoying to think, "Well, I'm a monk, and maybe there are these iconic monk abilities that I have to wait till second, third, or fourth level to get, just because we didn't want someone stealing that."
Noonan: Right. In other words, the multiclass rules place some significant constraints on class design--
Mearls: Exactly.
Noonan: --and really, class is primary to D&D, so you want to let classes be as unfettered as you can manage.
Mearls: Exactly. And that's sort of the big change; because even when we designed it, we did build the classes first, then said, "How can we make these guys multiclass?" Because we wanted--the class is the heart and soul of any class-based game. If they're not interesting, then the game isn't going to work.
So, now with multiclassing... it's still in. You can still combine classes. It's just a little bit more, I guess I'd say, controlled. We are actively designing the benefits you get when you multiclass. You're no longer just looking at the class advancement table and copying stuff down. The rules more dictate, "Okay, you decided to multiclass into fighter, here's what you get because of that." If you want to go further, then it says, "Okay, you're deeper into fighter, now here's what you get."
So that allows us to let the class table and the class features function properly. And then, the interesting thing, that lets us say, "Well, what does a multiclass fighter actually learn? And then at what rate?" And that doesn't happen at the same rate as what the class is giving, so it gives us a little more flexibility in design.
And the nice thing is that since we have more control over it, we can make things like the fighter/wizard work more effectively than, say--oh, rolling up a 10th-level guy, I only have caster level 3--it's hard to make that work without spells specifically designed for that character.
Noonan: Yeah, I think... speaking as broadly as possible about multiclassing, I think it's accurate to say that it's more flexible in terms of "splashing" the multiclass, of splashing a second class into your mix. It's probably not as flexible as in Third Edition for sort of "deep" multiclassing. However, a lot of those "deep" multiclassing options in Third Edition were bogus. (laughs) I mean, would get you killed in the dungeon. A wizard 5/cleric 5 is in big trouble in a 10th-level dungeon.
Mearls: Yeah.
(And my God, those guys talk fast. My respect for professional stenographers just went up by a factor of several hundred. I type 89 words per minute, and I had them playing back at half speed, and I was still having trouble keeping up.)