I am pleased to announce that 5 years after my post found here (where I threw in the towel early):
https://forums.macrumors.com/threads/macbook-pro-802-11ac-upgrade.1521466/page-4#post-18438927 , native 802.11ac WiFi is working on classic unibody MBPs!

All of this was performed on a Mid-2012 A1278 13" MBP with Mojave 10.14.3.
This upgrade should work on the following models:
15" - Mid 2010 through Mid 2012
13" - Early 2011 through Mid 2012
I was encouraged by several members, most prominently,
@highvoltage12v , who said the iMac cards from 2015 have the proper IPX antenna jack sizes on the card for the classic MBPs.
I reused my original adapter board I luckily kept from 2013, and lo and behold, it all works!!

Now that the prototype works, the current plan is to make the adapter more compact and robust without using Apple's proprietary Airport connector.
If there is enough interest in this by members, I plan to launch a Kickstarter or an eBay store.
Photos and screenshots:
I am interested. I just posted this;
https://forums.macrumors.com/threads/2012-macbook-pro-wifi-fail-please-help.2175801/
But I'm interested in your project. I would sure like to get my MBP (Model A1278) up and surfing asap so any suggestions for a WiFi card would be greatly appreciated. I could upgrade to your AC unit at a latter date? Keep up the good work! Thanks.