Sometimes I think about it. Lately the number of players in Phantasy Star Zero is an average of 3/4 players per day [tested this in 2 weeks] and usually japanese people. For a DS game, for sure there is still a small demand.

But there are several other DS games that nobody plays for months or even years in online mode [Luminous Arc 1, Contact to example a few]. PS0 will continue even when the Nintendo Wi-Fi Connection go offline someday?