Indeed.
At most, this film probably wouldn't be more than 2 Hours and 25 Minutes. During that time, they have to catch audiences up with what's been going on for Superman and company since the conclusion of "MOS", while dealing with the fallout from Zod's invasion, introducing Bruce Wayne/Batman and his world, along with bringing in the likes of Lex Luthor, Wonder Woman, Aquaman, and Victor Stone in some form of fashion.
We also have to deal with the inevitable confrontation that Superman and Batman will have with each other before they eventually put aside their differences and work together to take down a bigger threat, thus the beginnings of the Justice League.
To cram the "Death" story line into all of this would be a HUGE disservice to it.
One of the reasons why that story worked so well was because Superman had not only been around for a long time within the DC Universe, but because of the long standing relationships he had with everyone that was shown to be affected by his sudden death.
Superman's death will mean a hell of a lot more if he's been friends with Batman and company for years, while having been a part of the Justice League already and being hailed as a hero by mostly everyone on Earth.
Killing him with the excuse of saying that people who once hated him will now realize on how important he was is a weak one in my honest opinion.
Honestly, I would rather wait and allow the DC Universe to get fully formed first before I play out a major story line like that. Other wise you end up not only wasting that story line but potentially harming the much needed development that the DCCU needs right now.
Heck, one of the reasons why I feel "Days of Future Past" had worked so well is because we had spent several films getting to know the X-Men and had a least one film devoted into showing the younger cast/generation as well.
I really doubt that people would have been "as" invested in the final product if DOFP was the first time we were seeing James playing young Charles or Michael playing Magneto for the first time.
We got to know the casts of both eras so well that it made the story feel that much more important and invested in.