^ They just won't be legacy characters anymore. Instead of, for example, Jay Garrick starting the Flash legacy and it passing to Barry, it will now be Jay Garrick, the Flash of Earth-2 and Barry, the Flash of Earth-[insert number]. Different characters with the same name.
The more I think about it, the more I am coming around to the idea. If they are in an "Earth-2" scenario, it might provide an opportunity on DC's part. Depending on the success of the JSA book, it would be neat if they treated the Earth-2 as Marvel treats the Ultimate line. If it can support a few spin-offs (best case scenario, of course), have it be a separate line from the mainstream books with, perhaps, its own overall arc building to some Earth-2 event. The difference would be, of course, there wouldn't be any mirror characters (ie. a Earth-2 Superman, Batman, etc).
I guess my point is DC has an opportunity to do something unique/new with the Earth-2 concept. Before it outlived its usefulness and the shared universe, to me, was the better route. Now, that they are building it from the ground up, perhaps it can be made into a much more workable concept.
At the same time, it's time to separate the JSA from WW2. Seriously, I don't know why people think they belong in that time. On the DC forums, someone called it their "golden years" or "greatest moment".....
Why?
Yup. It's stupid and pure fan service that those characters are continually tied to WWII.