I will add my experiences FWIW.

I started out with the plan to do this full retrofit but after looking at a car on the show floor decided to just do part of it - namely just the floor 51477360761. IMO the storage bins are so tiny they have limited use and the rest of it isn't all that critical unless you really think you need to prop up the floor or tie down something. Everyone has their own uses but since I did this, I haven't looked back or felt like I wish I had X from the kit.

Anyhow, to your actual question around the 12VDC power port, I did put something like this in - but I put it into the back seat so passengers could charge phones and so on and I just went with a USB port instead of a 12VDC, I simply ran a pair of wires up to the center console where there is a 12VDC outlet and tapped into that using snap-on taps. I then just drilled a hole in the rear of the center console and called it done. No issues with the power port being overloaded. If you decide to get the official power port for the trunk I think you'll have to do the same since as I have found, in the infinite wisdom of BMW, if the car doesn't have the option they don't put the wiring in. IDK why they bother since you would think having one wiring harness would be more cost effective but it is a frustrating part of the car.

I wish I had taken a few pics of the front center console but it basically isn't much to look at once you pull it out.

I used this unlit USB port:
Hope this helps!

https://cimg6.ibsrv.net/gimg/www.nor...dc772b5f87.jpg
This is what is underneath the rear cover, just enough room on the lower left to snake through wires and fit the USB plug.
https://cimg4.ibsrv.net/gimg/www.nor...babd013b78.jpg
After everything was installed.
https://cimg5.ibsrv.net/gimg/www.nor...2cea1c2536.jpg
Added a key fob logo to the cover

Thats cool, i was thinking someone could make rear heated seats with a universal heated seat kit.

https://www.ecstuning.com/b-dorman-p...nterior-seats/

or

https://www.ecstuning.com/b-metra-parts/v-Mini/

Sweet setup. 🤙🏽

I’m in it for the false floor and the upright position for the back seats…both for the comfort of the dog. 😅

I found part of the wiring harness for right and left trunk from a junked f54 with the storage package, so if I get ambitious maybe I’ll swap those out to get a working power socket back there. The left side trim is currently hanging me up, can’t find one in the states at all. 😕

Please help me catch up. I'm going to buy a MC 4 door which doesn't have the storage package.
The element I'm interested in is the floor that can have two positions.
Is that adjustable floor I'm interested in the same as the "false floor/hidden trunk cover"?

Yes, I think so.

P/N 51477360761 (false floor/hidden trunk cover)

The floor is one piece that has a fabric hinge in it to allow for access to the area just inside the rear doors/bumper without having to raise the entire floor. Once you raise the entire floor you can get access to the "spare tire" area. The floor raises/pivots in the back via two plastic clips which go into the frame. If you want the floor to actually stay in the open position then you also need to replace the trunk sidewalls which have retaining clips in them which is a lot of effort/cost IMO. It is the clips that give it a second "position" (open) with the other position being closed flat on the floor. If you think you need the second position for something regularly then it might be worth the investment in new sidewalls but otherwise I would suggest just going with the floor only.