From my 1.5 year of selling a few accessories for GIulia/Stelvio, I know that 90% of customers won't will to cut wires, expect plug&play with clear instrucitons. WIth headunit it is not that bad, as you may buy some 1:1 compatible looms, and cut on production withi that offering plug and play. Bit of problem is that such looms are chineese quality - I had installed a few AA/ACP boxes to GIulia/Stelvio which used similar approach, and had issues with them - either too tight contacts and lever was getting bit damaged/ didn't wanted to close etc, or too loose contacts and e.g. on bumpy roads right channel was disapperaing etc. Looms still adds labour and some cost (mainly getting that done right, you won't be manufacturing in China for cheap, but in EU low volume, so expensive). Also testing - you won't be testing every unit in your car, so you need built automated tester which verifies all is good with all connections and functionality. You would need spare tester just in case, and cables to buffer tester and avoid using its connectors too quickly (better use some addtional cables and replace them after say 200-500 units tested). All adds custom development cost (just 2 testers and cables and their firmwares and documentaiton).
There is numer of my products which landed as prototype only on my car and a few friends or say one customer max, but I never decided to go for production. Most were too expensive to build/release properly comparing to volume, and a lot also would require homologation (yours maybe would sleak wihtout homologation, can't say for sure). You are also taking responibility whenever anything happens to the car, customer first ask you if it coudl be the device, or people start noticing after installation things they didn't pay attention earlier (but standard on GIulia/Stelvio) which they only noticed some time after installation of device.
Anyway, congrats you made it, if you decide to release it for sell, I'm happy to direct to you others, I know a few people on Polish forum who would like to upgrade their old rev headunits with 2nd gen for OEM AA/ACP, some already have headunits waiting for solution.