A Rivendell isn't a compact geometry bike at all. A compact geometry bike has the head tube in the traditional position and the top tube slopes downward creating smaller frame triangles. A Rivendell is sized at the absolute largest frame one can possibly stand over, including with some 'discomfort'. The top tube does not run down from the head tube, so much as the top tube runs up from the seat collar to an elevated head tube. Much like what a bike with an add on Serotta Heads-Up looks like. However, almost all Rivendell bikes go out the door with beautiful lugged quill stems, or Nitto Technomic quill stems. The founder of Rivendell definitely is NOT a fan of threadless.

Zinn definitely incorporates compact geometry principles into his Project Big bikes. He also uses elevated head tubes. Zinn stocks carbon forks with 450mm steerer tubes. However, the reason Zinn utilizes compact geometry has nothing to do with the extended head tubes. The compact geometry allows the fabrication of very large frames without having to use as much frame material, granting all the benefits of a smaller compact geometry frame, only with increasing returns of stiffness and lighter weight. The elevated head tube has nothing to do with the use of compact geometry. You can use an elevated head tube on a classic geometry bike (Riv does, Zinn did, and does).

You can extend the head tube of either a compact geometry bike or a classic geometry bike with a head tube extension (either a Serotta Heads-UP or a similar product).

At the end of the day an extended head tube (or not) has nothing to do with compact geometry.