I remember reading that Bruce Timm and co. were creating offbeat ideas for a Batman cartoon series before Batman Beyond was created, because that's what Kids WB and the toymakers wanted. He pitched a heavily anime-inspired take on Batman, a Justice League series idea that was more like Teen Titans, because Batman would be in charge and Cyborg would've been a member.
Basically, he was pitching the most toyetic Batman cartoon concepts possible, and Kids WB were like, "Nope, don't like it", until the idea for Batman Beyond came along.
Can someone else fill in the rest of the details I've missed, if any?