Ultimate DIY speaker design?

The problem with any of the Wilson designs would be the cabinet. There is no way you could possibly make anything like the one they have outside a dedicated factory. I know you said no kits but I would look at something like the Prestige model on the Wilmslow Audio site. It's drivers are very possibly better than the ones Wilson uses and the cabinets are MDF, although VERY heavy. I would think about getting some made myself [my woodworking days are behind me] if my room was bigger. You can substitute other drivers in any of their designs, which are only departure points, and they can supply the crossover, which is often the the point at which DIY designs break down. There is a fascinating site on the web by someone who is probably the ULTIMATE home builder, I will try to look it up and post it. He builds things WAY beyond anything which would be economically feasible to put on the market. Since you are not bound by the same constraints as manufactures you should not limit yourself to copying their products.

Look at Jack Bouska's Weblife site if you want to see some amazing DIY speakers, audio porn is the only term for them.

Remember the post of a guy who built massive horns into the foundation of his house? I think these were almost big enough to crawl though.

Start with a DEQX for dynamic drivers or a Wisdom DCAB-1 (if you can find one) for BG (Bohlender-Graebner/Parts Express) ribbons.

Check this one out:

http://www.soton.ac.uk/~apm3/diyaudio/Amaticlones.html