You know what? Spielberg's right. The comic book genre will implode. But its not JUST because of the MCU. Its because there are tons of comic book movies out there. It's called oversaturation. Eventually, they will reach a point of diminishing returns. Then they will come back, but perhaps be a little more tempered. It has happened with nearly every film genre there has been. Look at the westerns. Hell, look at STAR TREK.
Yeah, the DCU could be dangerous. Not because it won't be any good (although I have real doubts) but just because it will be more superhero films.
Then again, westerns were around for a very long time and most of them weren't particularly good...
I think Marvel is the one who will oversaturate the market, not DC.
The biggest part of Marvel's Phase 3, is that they will be releasing 3 movies a year, instead of two. Just look at the list.
Captain America Civil War --- May 6, 2016
Dr. Strange --- November 4, 2016
GOTG 2 --- May 5, 2017
Marvel's Spider-Man --- July 27, 2017
Thor Ragnarok --- November 3, 2017
Black Panther --- February 16, 2018
Infinity War Part 1 --- May 3, 2018
Ant-Man and Wasp --- July 6, 2018
Captain Marvel --- March 8, 2019
Infinity War Part 2 --- May 4, 2019
Inhumans --- July 12, 2019
3 Unnamed Movies for 2020
Add in the Sony/Marvel Spider-Man solo movies and the Sinister Six movie Sony still wants to make happen, and you've got your recipe for crash right there.
Fox will more or less be out of the game after 2016, when
Deadpool and Apocalypse come out. After that we have Old Man Logan, Gambit and New Mutants. All of which have been announced but none have started preproduction or have scheduled release dates.
WB has their films, but they're spread out to be either summer movies or winter movie release dates. While Marvel is staking a claim for winter dates, summer dates and early spring (February/March) dates for their phase 3 movies.
It will be really crowded, either way.