My concern with the Crisis on Infinite Earths is that I almost think they (being the producers) have put themselves into a predictable outcome. Either one of the following will most likely occur:
A). Kara and Barry will die as they did in the Comic version. But, because both are the stars of shows that are ongoing, they both will have to somehow be revived rather quickly. Which, if not done very well, will invalidate anything they did in the Crisis and will leave fans disappointed.
B). Oliver Queen will take their place and die because that show is ending and his death could be considered final. In this scenario, it will seem almost like a cop-out that Kara and Barry weren't sacrificed.
Either of these two scenarios is predictable and so, I'm not sure how they will be able to spin this to create much apprehension. Maybe it's just me (which is very possible), but I am always more interested in seeing something new, something created out of the writers imagination that will leave me on the edge of my seat, not knowing what will happen and how it will end than to see an established story that has a predictable ending.
C. Of course, none could die and in a way, that would be a complete let-down. I know, I'm hard to please.
One thing that I don't want to see happen is a merging of the universes. I like Supergirl in her own world. I haven't seen a cross-over yet that has utilized her the way she should be - she always has to be nerfed big-time and having her in the same universe with so many other superheroes will just compound that problem. Plus, it brings in the complaints of - well, why doesn't Barry come and help? or so and so?