Well, considering the style of the series, and that Aoyama sensei already said that it will be a happy ending, i suppose this will contain:
-ShinxRan relationship: probably a marriage, an engagement, an official relationship (from the last interview with Aoyama-sensei, i think were gonna see a kiss, and probably an official relationship before the end of the series).
- BO taken down: I suppose a lot of members will die, specifically the Boss, who seems to be very dangerous to just go to the jail.
- Probably some "good" character will die: im thinking about...Akai?...well, probably not...probably no one of the good or main characters will die.
- All couples relationship: it seems so obvious to me that Aoyama will put all the couples, officialy together: HeijixKazuha, ShiratorixKobayashi,and maybe, ErixKogoro together again too.
All this points, specially the last one, seems so much happy ending and i wonder if this will be good. Anyway i just think that everything is gonna end up fine sice DC is not such a dramatic series.