Dreamcast must have been the platform chosen to continue the development of NeoGeo games after the "death" of AES. Despite having an optical platform, because of its speed and RAM memory there were great conversions (Last Blade 2 / Garou) and greats re-makes (KOF98 & 99) for DreamCast and spiritually it is for me the next arcade platform (Naomi) after MVS having the Capcom VS SNK and other fighting hits that were seen in the last arcades that were still opened after 2000.
As for whether it's dead, the FAN base is not as hardcore as AES but there are still some developments for it and I think it's a must if you were a fight and non fight arcade lover in the late 90's, early 2k (and you don't want to buy a lot of different arcade boards)