Would Crisis 4 be Infinite Crisis with Superboy Prime and Alexander Luthor as the big bads?
I am not all that familiar with the storyline but I know it was this that triggered Jason Todd's revival and it also involved Power Girl so you could introduce those 2 as the playable non-crisis heroes.
Power Girl is already in Crossover-1, so it's doubtful (but not impossible) for her to be included in Crisis-4.
So far the only 'reused' Super Hero is Starfire, and that is partly because she was a Promo the first time around.
There was some good stuff with the Teen Titans from Infinite Crisis that went down. As far as characters and main deck cards I am betting Crisis 4 will be based on The Outsiders with maybe a little Young Justice sprinkled in. The Outsiders was kinda the parallel "young" team during Geoff Johns TT run.
They've been making more and more effort to tie the Crisis packs into the matching base-set lately, so Crisis-4 will likely be 'teenage hero' based.
If they stick with a Titans theme, then Donna Troy is where I'd bet my money. She's the last of the 'big names' to not have a Super Hero card (let alone a regular hero card).