Actually, it is more likely that the blue Machins would be doomed. That would happen if Ofcom, the current postal regulator, returns Royal Mail to a single class of inland letter mail. The December issue of Stanley Gibbons Monthly reports that Ofcom took a survey, and a majority of respondents were in favor of a single class of mail that offers two-day delivery and costs less than the current first-class rate. I believe the current first-class service offers next day delivery, and second class is two to three days.
The two-tier mail system was introduced in 1968 to help balance the post office’s workload. With only a single class of service, all mail had to be processed at the same time. After the introduction of the two-tier system, the second-class mail could be processed at night, after the first-class mail was finished.
Perhaps modern automation no longer requires such separation, and a single class of mail would be more efficient for the post office and, apparently, more desired by mailers.
I would guess it’s a long road from here to there, but if it happens, there would be a lot fewer Machins for us to collect.
(I linked to the Stanley Gibbons site, but you cannot read the magazine without a subscription.)