Interesting customizations. I use 805's - not the best trail sole, IMO (807's are better), but purchased some on closeout some years ago for $30 a pair.
>>"Not sure what the next step is yet."
Second step might be to look for stress concentration points in the reworked design. For example, just below the '7' of the 807 where the 'now' heel-strap meets and connects with the sole of your new 'eight-oh-shandal/shodal'. Each step will cause the heel strap to want to rise up just a bit, putting stress at that [new attachment] point. After how many thousands of steps will a crack possibly start to form there? Curves distribute stress, so, all other things being equal, cracks take longer to form. Sharp angles concentrate it. Not sure at this point you could round off/out that point. Look for a way to reinforce that area with some additional material that will take up the stress and prevent a crack from forming there. If a crack starts to form there, it will probably propagate forward. [Brett, if you read this, i think that you've done some test work in your engineering career, maybe you could be more helpful here than i am.]
I'm just making a semi-educated guess that this could be a problem area. This is not meant to discourage you, but rather to help your design succeed, which i sincerely hope that it does. Most good designs have many failures first, so don't get discouraged if your first design doesn't perform to your expectations. Each flaw/problem is just an opportunity to improve the design, that's all. Looks like you've made a great start. Keep up the good work.