I do not think that many would purchase a DS version of Pac-Man Vs. simply because the price would probably be at least $15. I can't see Nintendo/Namco selling a game for less than that, no matter how bare-bones it might be. If they made it part of another, larger game, then it would work out.
Though maybe this could be a good example of Wii/DS connectivity. The game could be purchased cheaply over the Wii Shop Channel. The only extra piece of hardware it would require is the DS itself and I'm sure plenty of Wii owners own one (or have a friend that does). If they made it online-enabled then the need for a DS is eliminated (although the game is probably more fun in the presence of friends).