  High Luminosity upgrades of the KEK-B collider are being discussed. We
consider the role of the purely leptonic decays B^\pm -> l^\pm nu and B^0 ->
l+l- in motivating such an upgrade. These decays are very sensitive to R parity
violating extensions of the MSSM, and we show that future runs of the KEK-B
factory can be competitive with high energy colliders for probing such models.
