So I found you can also retrofit the OEM power lift gate it appears with public toolbox, and of course the towing package. Theirs also an option to change battery type to lithium ion for the 12v. This might mean an updated Intel MCU than runs on 16v may eventually be available for retrofit, or possibly Tesla will support a scaled down amd upgrade for older cars someday. I didn't want to change the type and find out
It looks like you can replace hv components, if you can buy them lol and even reprogram battery packs with toolbox. Swapping computers for the same type I imagine is possible too if you read the config and then write it, but I don't see any options other than autopilot upgrade for official retrofit scripts.