Just wanted to post saying that I'm very impressed with your work. I don't personally own an M54 engine car (anymore), but I would definitely buy one of your DISA units if I did. I think one product that would sell really well (better than the DISA or CCV fixes) would be some kind of permanent solution to the expansion tank problems.
If you ever decide to start making products for other BMW engines, do consider taking a look at the cam-bolt issue that S54s go through. Sometimes it's referred to as the "VANOS bolt" issue. It caused catastrophic failures in several M3s (and probably other S54 equipped cars), and the rest of us check our bolts every 15-30k miles just in case. I'd gladly pay for a permanent solution, even if it cost as much as $500