Re: designing a better kit frame.
 

the primary reason for using a chain tensioning and wheel lowering system that does not slide is reliability and ease of use. sliding bearing blocks are an ideal solution, however they do just that, slide. i am un-inclined to trust anything that slides in that manner. many bicycles made use an a-centric bottom bracket, one of my team-mates bicycles was actually the inspiration for these. a sliding bearing block makes it possible to over-tension chains very easily. however with these, it will be more difficult to over tension the chain, with the addition or subtraction of a half link, and the rotation of the block, any length of chain can be tensioned.

Re: designing a better kit frame.
 

While the tubular pieces are interesting, I would be concerned with the amount of machining that they entail. In order to consider them as a KOP option, I would think they would need to be molded plastic (which could reduce the weight even further without impacting the strength). I think the real merit of the design is the modular bearing block with a-centric holes. Even a tubular frame made of 1" square tubing could utilize these bearing blocks effectively for all the same reasons that you quoted.

However, as you stated in your earlier posts, the preference is to have dead axles for all but the inner driven set. These would not need bearing blocks as they are dead axles. Using a shoulder bolt for supporting a dead axle is really all that is needed so maybe these a-centric mounts would come in various options:
1) True bearing blocks for driven axles
2) 1/4-20 clearance hole for the threads of a shoulder bolt
3) 1/2" clearance hole for shaft of the shoulder bolt

Just some ideas if you really want to take this to the next level.