First, I'll address the idea of Christian Bale being Batman in the new DCCU. That can't work. Why not? Well, Nolan essentially made a complete and self-contained thing with the Dark Knight trilogy, and Christian Bale is the definitive Batman for that brand. Bringing him into a different universe always runs the risk of associating that brand with the new Brand they're to build, that's just the reality they had to grapple with there. Secondly, The Dark Knight Returns is a pretty prolific storyline that exists and is pretty good (or at least it is according to most people who'd tell you that it was a gamechanger in comic writing. So the aging Batman thing isn't new, it just hasn't been done on the big screen), so I don't necessary think there's much of problem with giving us that type of Batman interpretation, especially bearing in mind we've never gotten this interpretation on screen yet. Mark my words, Ben Affleck is going to be the definitive Batman for a few generations to come (if the movies are good). Batfleck might even direct the next Batman, which is an interesting prospect in and of itself.
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And now, the differing philosophies of Marvel and DC when it comes to how expansive their universes are.
Here's the thing (take my contrary 2c for what they're worth). There are so many things to consider here.
Firstly, what Marvel has works with a connected universe for multiple reasons (I'm going to refer mainly to the Disney Umbrella as opposed to the Fox or Sony stuff). Firstly their, cinematic universe as started by the Iron Man movie has largely had a good number of hits which has allowed the brand to expand said universe into the TV realm with shows like Agents of S.H.I.E.L.D, Agent Carter, Daredevil, Jessica Jones (these last two, by the way, are street level heroes by the way, which is important to remember).
Now yes, they're all in one universe and if you're a dedicated fan, that's great if you're concerned with continuity and the like, and that's the positive side of things. The negative side of the coin is that the TV universe (Agents of SHIELD in particular) feels constrained somewhat in terms of what they can do plot-wise because of the movies (Daredevil, Jessica Jones, and the coming Netflix offerings have avoided this largely in part as a result of the somewhat self-contained nature of the Netflix universe with the odd tie-in back to the larger universe). So in my opinion, the tie-in of shield to the larger universe has hurt it somewhat (I watched season 1 and part of season 2 and it felt lackluster... but that's just my subjective view). But overall Marvel has found a formula that works... for them. Please note, pre Iron Man, Marvel had just as many troubles in terms in terms having a bankable thing (Ang Lee's Hulk, the Daredevil movie, etc)
DC on the other hand have opted for a different approach, letting the TV and Cinematic universes be separate from each, and at first glance it sounds like a flawed plan, until you consider that regardless of Nolan's Batman trilogy (and maybe Smallville with the cult fandom, which I'm a part of

), in recent years DC's name isn't as trusted as Marvel's is. So it doesn't surprise me that they wanted their TV properties to have no creative shackles as a result of the cinematic universe (honestly, like look at what The Flash and Arrow are doing right now because they can tell the stories they want to tell us about whatever incarnation of the characters they're selling us). As reader of both publishers' comics DC catalogue probably has more elseworld tales than any other publisher, which means there's a plethora of stories to pool from in the source material, which means we as viewers can get even more stories with different interpretations of our favorite characters. So for example we're going to get Ezra Miller as The Flash in the movies and that's fine, because as much as I love Grant Gustin, I'm keen to see how they interpret him in the movies vs the show (because the comics themselves have different interpretations of each Flash, and a lot of the other characters). I mean some of my favorite Flash or Superman stories aren't even in the same comic continuity or by the same writers.
tl;dr (I'm rambling), Marvel has found THEIR formula and it works for them, and the upside is a continuity that spans over a vast array of properties and characters, but it runs the risk of shackling creativity of the network shows like Agents of Shield. While DC have chosen to give the TV and Movie universe a bit more freedom by separating them, which might have us seeing similar characters in TV and cinema while having a wider variety of stories and character interpretations to enjoy. And I think that's a formula that'll probably work out better for them as opposed to Marvel's formula, especially considering that even their comic book history and philosophy is somewhat radically different. Basically 20*5 = 100, 25*4 = 100, 1000/10 = 100. Essentially, neither Marvel or DC are infallible, but I think fans give them less credit than they're due for the logic or thought process behind some of their decisions.
P.S. I've never understood why fans are afraid of different interpretations of characters and different adaptations of stories, especially in comic book movie genre, where the source material itself is notorious or famous (depending on how you look at it) for doing that very same thing.
P.P.S. I'm not proclaiming to have definitive answers because I could totally be pulling things out my ass, but I just feel like fans in general are somewhat dismissive in their opinions at times, and need to be a little more open minded in their processing of this stuff.
Addendum A: [MENTION=4613]TheAvenged87[/MENTION] and I had a similar discussion about this way back:
I think I'm a bit dillerious at this point. I haven't written a "2c" post in a loooooong while.
EDIT: Seriously, read if you dare.