I was able to spend a little more time on my desk this past weekend, and got it nearly done:

A quick changelog:

Added a frame to the desktop. I'm planning on using 1" phenolic resin (or *maybe* epoxy resin, if I can afford it) for the surface, and it needs to span almost 5'. At that length it seemed like a good idea to support the span, and I'm using an 8020 frame to do so. It's not the cheapest option, but means that attaching the surface will be easy. It also has the advantage of allowing me to attach other accessories (a power strip, my monitor stand, an architect's lamp or two) really securely as well.
Added adjustable feet. These are nylon with a rubber pad, and they thread into nut inserts that'll be installed in the leg caps.
Added shelf clips to hold the lower shelf onto its supports. I think that the shelf will just rest there - the clips should snap more or less securely onto the supports, and I don't think I need to attach them any more firmly than that.
Other small changes to the leg brackets. I had an early prototype printed by Form Labs in their "Tough" resin, and was pretty impressed with the results; the part came out true to size and clamps onto my carbon fiber tubing really well. I'm having a few more parts printed now, and will rig up a bigger test assembly to confirm - but with the combination of my leg geometry and the Form Tough's high tensile strength and elongation at break, I'm confident that it'll work well.

Time allowing, I'll order the rest of the stock and cut-to-order parts in the next week or so. Pretty excited :)