A lot of this is speculation at this point – we have no idea what DC/WB are planning and therefore its really way too early to say something is rushed or crowded. But these are some logical assumptions and thoughts I’ve made as to why introducing Batman and Wonder Woman in the Man of Steel sequel is an overall good decision.
1. Avoids an Immediate and Unneeded Solo Batman Reboot
Given the fact that Nolan’s stellar Dark Knight Trilogy ended in 2012, its still way too soon for Batman to be given another solo film and especially another origin story. Thankfully, Batman being introduced as a more world-weary, untrusting, and semi-retired hero in Man of Steel 2 (or whatever its called) eliminates the need for another “young Bruce/Batman” origin film and thus lessens any comparisons between the new Batman and that of Batman begins. As Kevin Smith and several others have pointed out - this will be a very different Batman than we may be used to seeing on screen. Having Nightwing as a cameo will also help create the sense that this is a Batman who has been around for awhile - someone who is much more experienced than the very young and learning Superman. Narratively Batman makes sense to be introduced at this point.
2. Expands the DCCU and Creates a Shared Universe
At this point we don’t know how large Wonder Woman’s role will be - but having her be part of BvS/MOS2 is a smart move as it introduces the audience to her character and the actress playing her – thus not risking possible failure with a solo outing – people will be invested in a future solo outing because they introduced her in BvS (a movie that is guaranteed to be a success). Having Batman in the film further accomplishes the same goal and also-
3. Lays the Foundation for a Justice League Film (plus solo films)
With Superman, Batman, and Wonder Woman all appearing in the same film (in unknown and varying capacities) we will have the “Holy Trinity” of DC Comics on the big-screen. And with that - once the trinity is revealed - this will lead smoothly into a Justice League film (rumored to have a release date of 2017). As Del Toro said several months back - DC/WB has plans for the entire DC Universe - and that undoubtably means solo films at some point. Its different from Marvel’s approach and I think thats fine – thats a good thing. Its necessary at this point.
4. Develops Superman as a Character
Man of Steel (more so than any other prior big-screen appearance) truly explored and developed Superman and Clark as a character. Through themes like identity, alienation, trust, and ultimately the effects of a Superman figure on the 21st century, we really got insight into the character. The sequel will undoubtably follow this trend. In contrast to a Batman who always initially believes Superman is a threat, it will help transform and develop Superman as a character.
Of course we won't know how good of a decision it is until the movie comes out - but for now, in my opinion, introducing Batman and Wonder Woman is good.
Thanks for reading!