i've heard of coconut husks as media, i suppose any kind of nut husk that doesn degrade or swell with water, or attract mold/parasites, is a good media
The husks will probably change your Ph.
Just want to make sure that the nut husks don't give off any chemical that inhibits plant growth. I know some nut trees tend to inhibit certain types of plants but I don't know if that property would extend to the nut shells.
The biggest problem with "organic" material as media is that it can rot, break down, hold too much water, turn your water dark colors, and affect pH. Even Coco Coir which tends to be slow to break down in soil applications tends to turn into a mucky soup fairly quickly in aquaponics. (The nitrogen rich water tends to be a natural compost accelerator.)
That said, I won't tell you not to test out the idea, However, know that you are testing uncharted territory and no one here can guarantee your results.
I too think it is a worthy experiment. I have experimented with husks, straws and crushed nutshells and walnut shells were the best. I have no experience with Hickory nutshells though.
* none were acceptable for long term growing.
This year I experimented with different kinds of straw in different combinations for my wicking beds. The best result was a combination of 50% wheat, 30% barley and 20% corn stalks. The best result was when wheat and barley was woven at diagonals to vertical cornstalks and then two sheets were sewn together.
I use the shells for other purposes too. Hickory nuts are almost as valuable as pecans. Some info. I keep a 100 lbs or so stored for emergency food supply, the husks I burn in the firplace and I also use them to smoke meat. I think I will see if someone from Purdue will help me do a study. What I dont use goes on the compost.
I do beleive your right about the PH TCL.
I will post my results!