If you are thinking about coating the fines with a slip and then forming it in a mold there would likely be a couple factors to think about. You will reduce the space between bits of straw and likely make a material with a heavier clay content that absorbs more water and dries out more slowly.
If you wanted to form a wall with it, that would mean shorter sections in incremental pours.
too little clay in the slip and the risk of fire would increase, as well as reducing the normal clay as cement effect.
It does look like neat stuff to play with, and the only way to understand it really well is to try different things with it.
It would also probably work really well in a first coat render if you pulled out some of the bigger bits.
There are probably lots of cob enthusiasts who would love to have access to that material. Cutting straw can become quite tedious
At any rate, congratulations on your good fortune. That straw could be excellent mulch, carbon for a compost pile, and even as a cover instead of sawdust in humanure toilets.
Hi Michael and welcome to Permies!
From my experience, the straw fines are often mostly composed of leaf blades rather than stems which are hollow and provide the trapped air space needed to make it insulative. It would certainly work, but would not be my first go to source for a light weight higher R value material. As Bob pointed out, its great for many other things though so still a good score!