I don't see how this will pull players away, people have a choice to connect to either. If it does pull people away(in such a way that they stop connecting to disco altogether) it'll be the ones who have lost interest in discovery long ago, and the way I see it wanting those people stick around on disco is just to keep arbitrary numbers high. To make it look like it's more active than it is. Players who don't care about something are inclined to break rules and probably won't contribute. I am genuinely excited about this as it gives people something new to look forward to and will potentially introduce new people to the game and could even indirectly make new people come to disco as well.
I'll be sure to make the time to join the aftermath server when it's up and running. Best of luck, I can't wait