There are some aftermarket companies that already have power trunk and frunk kits, even with the foot sensing feature. Not sure what would be involved in a retrofit, but I would imagine you would have to run some cables + drill some mounting holes. The frunk design also changed to accommodate the heat pump and I would imagine there is quite a bit of plumbing changes as well throughout the car.
I'd be surprised to see Tesla come out with a retrofit path, as their primary focus is selling new cars. I recently went through this with Land Rover trying to find a way to get carplay integration, land keep assist, forward collision warning, traffic sign recognition, and adaptive cruise control into a Range Rover. The work involved for a manufacturer to design and support a path to upgrading just doesn't seem worth it for them. However for most of the options, they were available for my model year so it was a matter of purchasing the hardware necessary (forward radar module, mirror with camera, switches) and then reprogramming the ECU to turn on the features. Land Rover refuses to reprogram the ECU, but luckily there is a third party that offers a tool that can do this.
With the Range Rover the features stay enabled unless a dealer does an ECU update (which requires a physical visit). However, with Tesla, updates happen over the air and there have already been documented cases of features being revoked that weren't properly assigned to the vehicle's VIN. I don't see a winning path to trying to get around that.