Since Brock was there for Hoenn and DiamndPearl, a lot of the modern viewers would obviously miss him. But there are still a few original viewers, and I'm not sure of Japan, but I know that the western side love Misty. Most miss her. Some hate her, I know, but you can't please everybody. You can please most though, and like I said before, many miss Misty, and a lot of modern viewers (and original) would miss Brock. So if they had the original trio come back for a generation, that would get many viewers to watch, and actually might start up more talk about the Pokémon anime.