I think that when we put out the Crack-a-two-a, people thought a "souped up OTL headphone amp" was a Crack with a choke in the power supply and some 100uF film caps at the output. The performance improvements offered by the C2A are difficult to properly explain to someone who is hyper focused on what $50 in replacement parts can do, and really on that basis the kit wasn't all that popular.
There are lots of other ways one could go in terms of making OTL headphone amps, but whatever we would do would compete with the Crack itself, so doing a $1000+ OTL kit may end up being an exercise in futility!