Actually Tom,
First of all thank you for posting this,  I was thinking about intra block retarget last 4-5 months then I found your implementation.  My point was: if you want blockchain with 10mins block spacing, why you would like to hash and use x KW to do it between blocks?  I appreciate your white paper(bloody hell much more than I appreciate it).  I would like to see some stress test.
nyo_x