If DC were going to do these easter egg teases, they should do them either during the movie or at the end like in Batman Begins with the Joker card.
One really cool bit they could do if they were actually crossing their movies over (but they supposedly are not) is to have Green Lantern Tomar-Re present when Krypton is destroyed as he was ordered to delay the planet's destruction by the Guardians but was delayed when a star went nova and he was incapacitated.
I had the exact reverse idea for the Green Lantern movie where the destruction of Krypton would be counted by Sinestro as one of their greatest failures.
On the other hand. In the beginning of the movie when Jor-El is trying to convince the Council that the planet is about to be destroyed, he suggests that they could take the help of the Guardians of Oa but the Council calls them a bunch of fools.
It doesn't make it an idiotic idea either.
And there IS room for character development. Like I said before, part of the main selling point is seeing how they work together as a team. Stark still needs to mature. Thor is a god. Banner is a fugitive. And Cap's job is to lead the group. How does a man from the past lead a diverse team of people with diverse characteristics? How can you NOT see the chances for character growth there?
Also, 20 people won't be on the team in the movie. Its the main four with Hawkeye, Black Widow, and Nick.
none, after credit scenes are a gimmick that marvel seems to use alot. DC should 1up them and put the cameos directly in the movie, have the character actually do something, none of this after credits BS.