We have characters from Charlton, Quality, Fawcett, Milestone, etc.

Which characters do you think would best be served by actually being separate from the main DC universe? Difficult for me, because I have great deal of doubt there would actually be many stories with them in other universes, but presuming there were, I'd have go with Static. Which I guess would then extend to other Dakotaverse titles. I've only read Static and Icon. Icon, despite the duplication (as referenced in the World's Collide), could be integrated fairly easily into the DCverse, I think. He was so new as a hero, and appearing at the same time as others, that I didn't really get the sense of importance/prominence of Superman (that it took time for Superman to achieve). But Static got his powers from the Big Bang. I feel like on his side, the newness of what they are and their known presence in the world is important, and that can't really work with him part of a world that's known beings like this for a while. On the other hand, I'm willing to acknowledge that element of newness and change is something that would fade in time. Though, of course, in the long term it might make a difference if he was a first of fourth generation hero, but since I think of him as still a teenager, that isn't an element I've examined much. Full disclosure - I have read none of his Teen Titans appearances and don't know how that went.

Obviously, there are some characters that removing would have a much bigger impact on DC as a whole than others. Depends how integrated they are with characters from other origins. Though I wouldn't be surprised if the more integrated, the less fans though they needed to be separate to be really appreciated.

Then you have the ones like Dan Garrett - not really important to DC himself, but made important in the backstory of important character(s). And Ted himself was an import.