I don't know about the last bit. I know of our clients have extrenely clean, unabused f8x with no plan. Those cars are well looked after, serviced between 5 and 10k kilos (that is a much better service interval than one following bmws service intervals under plan).
So I'm saying it is to remove the blinkers. Motorplan doesn't isnt the be all and end all when buying an F8X.
There are clean examples that are not abused and are in even better condition than ones in MP
100% but also these cars tend not to end up on the open market unless asking for much higher prices that the wait list wasn't ready for or couldn't come up with. They trade hands without even being advertised sometimes. eg: My F10, S2000. If it has wound up at a strange dealer/WBC etc then there's probably some skeletons in the closet (imagined or otherwise). Plenty of examples here as well where guys come with surprise purchases that were never for sale anywhere. Recently, the 4C owners were all surprised to see one pop up for sale at a dealer since there was probably a full year of none being for sale at dealers, but plenty of owners changing hands and joining the group.
Plenty of guys waiting for the relationship to end and be first in line

as opposed to winding up on tinder and hoping for the best.
Nothing wrong with off plan cars provided you're fine with the occasional big bill and at this stage having motorplan for these cars is nearly off the table so condition and history will play a role.
Absolutely true but perception is something else altogether. Peace of mind..MP is massive..esp if the M car has mileage.
I would take a well loved car with some mileage over a car with a tiny amount of plan left and a clearly hard life for its low miles. With 2 or 3 months of plan left there is basically nothing anyone can really monitor and get done unless it was about to break already and BMW goodwill requires you to own the car for longer than that (unless you have a long history with them). I think these cars are non-starters for guys buying their first M or in some cases even their first 'fast' car that are probably going to be financed and probably stretching quite a bit into them. It is a big tax to pay for very little actual peace of mind
We (collectively) need to stop thinking the dealer service or only dealer touching the car is any more peace of mind other than a comforting lie. Consistency is nice. Being at the dealer is nice, but you 100% have to go through your car and check and double check work that was done under plan, clips missing, wires routed incorrectly or not secured through the right clips/channels, torque spec on your wheels etc etc. especially if it is not a very common thing that your car has gone in for. You have to do this whether it is at a dealer or independent or your own back yard. Interim oil services as well as Firi mentioned is critical especially on x35/40 and Ms and even when under plan.
I've said it before but people these days seem to have no idea how good a car with 100000 or 150000 or 200000km can look (and of course the mileage tampering crew takes advantage of this) because of what kinds of cars end up in the open market.
You can control the value you get by limiting your enjoyment of the car but, IMHO and experience, if you were doing 1000 or 2000km a month it wouldn't make a huge difference to what you would get if your car was in very good condition and is one of those cars that has a waiting list of next owners (whether it is for spec or condition). I sold my F10 with 140000km for around what cars with half that were going for and my S2000 with 88000km for more than cars with half that mileage were going for. Both also had aftermarket parts on them so keeping the car as low mileage and virginal as possible is one route to getting a wide audience and high value, but not the only route if you have guys lining up (and it wouldn't surprise me if you already had a few guys slide into your DMs to get onto your wait list now that you say you'll sell in a short while

).