Interesting discussion.
In my view we're on the cusp of an electric revolution for most forms of transport, which makes sense in a great many applications. We had an electric car for a few years and it was great, even with only 130 miles of range. Smooth, quiet, practical, well kitted, cheaper to run, better for the environment (after around 50,000 miles anyway), and so on. But totally devoid off any real driving enjoyment. They're a very good way of getting about. Once the silent acceleration giggle wears off, it's just an efficient tool.
For car enthusiasts, where it's as much about the noise, the vibration, changing gear and being the organic part of the machine, petrol cars will always be the preferred experience, as well as for the nostalgia hit, which is of course a huge driver for classic/enthusiast car appreciation.
Petrol will get more expensive, of course, £3, £5, £10 per litre, sure, in time, but people who crave the experience will pay it. It won't be for everyone. I'm not into game shooting, but people will still pay £10k a day to go do it. If you're able to afford it, people will pay whatever the rate is.
And in my opinion the M will of course grow in value in the coming years, 30k, 40k, 70k, probably 100k+ in 'x' number of years into the future. But as it rises it will price people out, meaning they'll then look for the non-M variant as the next best thing. That demand will increase, as supply continues to drop as a few more bite the dust each year, and so values will rise.
So yeah, the M will drag it up. Who knows what they'll be worth in the future, but for enthusiasts, who drive these not as dailies but for pleasure, the price of petrol won't be a blocker. If the M hits 75k in 10 or 20 years, the non-Ms won't still be sub 10k, they'll be following suit, just at the next level down.
All in my view of course.
Owen