I think for your expeditions and John's Tx200, the raisability (to use that term) is a key issue. And I really like the clever design with the slot for letting the pivot slide. Especially, since just pulling the downhaul keeps the pivot locked at the bottom end of the slot.
Although, why you are so down on wood and or fiberglass, I can't quite follow. I think it would be easy to replicate the functionality (and strength) of your design with those materials, while retaining the advantage of less weight on the transom. My rudder now contributes 0 (zero) to adverse boat trim, because it's effectively at neutral buoyancy (and that includes the weight of the tiller).
There is one (1) event here that I could sail if I had the DS measured. It's been called "day camp" for adults, and is supposed to be great fun, so while I think that the DS isn't a bot to win, even with handicaps, it's something that I don't want to rule out. Hence my reluctance to go outside class legal, despite the fact that the rest of the time it's been rather irrelevant.
Now, curiously, while I like the stock tiller, I have no kind words to say about the stock rudder blade. The foil shape is terrible, and, another thing that prompted me to replace mine, is the fact that it contains rebar (mild steel) in at least some iterations. If damaged, the steel will rust, and expand, and create cracks, letting more water in, for more rust...
On mine, as reported, there was also this entirely flat area at the top end of the blade that we exposed to the flow of water under the keel. I simply can't imagine that this contributes anything positive to the experience and in building a new blade, I was able to avoid that.
Now that you have the new rudder head, nothing prevents you from building a new blade. That would make the existing one your spare, which might in fact be handy. It's not that hard. A better grade of wood compared tow hat I used could result in a more durable design and for added strength, I'd consider the technique of cutting wide, shallow grooves down both sides and filling them with laminate (carbon fiber, for example). In addition to a full sheath of glass fabric, of course. But beyond all of those concerns, you could also play with some of the other parameters - making it deeper, for example, or deeper but narrower for a higher aspect ratio. See whether that improves anything or just shows uo the deficiencies of the CB more fully.