To piggy-back off of your cool project, I just completed installing passive key/push button/remote start in my Yukon.
Since I did not have an existing alarm system, my deployment consisted of three parts:
The passive key/remote start/push button kit:
http://a.co/csjbOor
As with any other kit, the wiring is a bit complex, but it was made easier by my next purchase...
The brains of the operation:
http://a.co/amVWCIi
I understand this is not 100% necessary, but it really made wiring everything up a snap. Unfortunately, I did not realize that it had to be programmed, which led me to my third and final purchase of the project...
The programmer:
http://a.co/dlrcx4B
This little hockey puck allowed me to program the brain, and made life incredibly easy. It defeats Passlock, initiates the lock/unlock process, and a few other features I did not use.
The Fortin device also had an awesome
wiring diagram that makes it Barney simple to do all of this magic.
Everything cost me about $240. I plan to sell the programmer since I'll likely never again use it, so hopefully that'll put my cost down to about $200.
As mentioned by the OP, you do have to disable the ignition shift interlock. It took me longer to separate the halves of the surround than to defeat the interlock.
Now my key fob stays in my pocket, I walk up to the Yukon, it unlocks. I get in, press the start button and away I go. I walk away and it locks... Very spiffy.
Next on my list is to buy a pair of rear door handles to replace the front ones (to eliminate the key holes) and to get my trunk button keyed to the Yukon for emergency entry. It is also worth noting that the starter kit I bought has this keypad that goes on the inside of the windshield. You can then type in a code (that you set) to gain access if the fob battery dies. Automagically the keypad works through the glass... No clue how that happens.
After that (and once this has proven itself for a few months) I will design and 3D print something to cover over the ignition switch... That way I do not need to actually remove it but can retain it in case of failure of this sstem.
I'm very pleased with the setup. Worthwhile and nearly invisible setup except for its convenience! Plus the remote start feature will be priceless as my company is relocating me to Michigan in a few weeks!