Do you think that harness of your design can be made by somebody as competent as you in numbers and sold at eBay or at craigslist? I am interested in buying one!
No idea if this would be worthwhile for someone to take on. The market size would be pretty small I suspect. I mean how many Accord owners would want to do this? My guess is only a handful. Lots want to go aftermarket so if Metra can pull their heads out of their backside or if iDataLink ever solves it, there will a large market for adapter kits that keep the upper display but don't require you to keep the factory head unit connected. But for now not many would want to extend their factory head unit to the trunk.
I'm certainly not interested in making this for others. I did it for myself and am willing to accept my substandard soldering skills. And if anything goes wrong in the future, I only have myself to blame. I wouldn't want someone to buy this from me and have it go south and they end up feeling like they didn't get what they paid for.
One of the reasons I was so explicit in the video and went step by step on how to do this, was to give those that are interested the confidence to try it themselves. If you're still not there yet, take my video to your local audio shop and show them what you want. Maybe they would be willing to do it for you provided that you picked up the used head unit.
Edit: But if you decide to tackle this, PM me and I can answer any specific questions, provide my wiring schematic, and help if you get in a bind. One thing to keep in mind is that I already have another harness that connects my steering wheel control, Kenwood head unit, and the factory 24 pin harness. So if you were going to start from scratch, you would need to either build that harness first, or just build a single one that accomplishes both objectives (tie in aftermarket and SWC and extend cables to the trunk.) Again, PM me if you have questions.