A quick update regarding the Schlumpf Speed Drive kit for Strida: I heard the first batch of the kit was almost ready. The delay of release was due to a redesign of clutch geometry. The change was deemed necessary to compensate for the higher tension on the belt (vs. a chain).
If the technical issue is indeed true, it helps to explain why Sports Duo has been produced in such a small quantity. But it may also raise a red flag on the durability of existing Sports Duos. 