It is never too late to look at a less expensive alternative. My impression is that since ACA did it for the Scout they know exactly how to proceed, whereas you are being led through a labyrinth by folks who have never done this before. You have no guarantee that they will approve your efforts prior to commencing an expensive test program.
ACA, on the other hand, has a template to follow, with almost guaranteed results. Costs would be the same or less, depending on who the DER works for. And they could charge semi-big bucks for a revised AFM, further offsetting their expense. You won't be able to do that.
Let's say ten of us would spend $500 each for IFR approval - that's halfway to completely cover my estimate for flight testing. The rest is paperwork, and again they just push a button and the printer spits it out.
Again, I would not go for it if it meant installing a specific suite of navigation receivers with TV screens, and they cut their market in half if they restrict it to metal spar wings. I bet they would get twenty orders the first day if they make it general enough.