I don't see any serious public calls for the removal of diesel trains for a bus replacement.
Charging is the questions. Marylebone-Aylesbury is definitely within existing battery operation range (80-100km range off the juice) and can charge off the Met (an exemption for the additional 2 lines of 4-rail may well be granted). You'd need some juice somewhere on the Chiltern if you wanted to use batteries via High Wycombe
Yes but you'd want to extend the 4th rail down towards Marylebone to maximise charging. At the moment you have 20km of a c.60km route juiced, so 15km dead, 20km live, 25km dead but in the unit diagram that turns into 50km dead, 20km live, 30km dead, 20km live. Rheostatic helps but really if you can get that down to 5-30-25 it's a much better balance, especially if you can install top-up chargers at the termini.
It's one thing having pure DMUs trundling through the countryside on quite branch lines, quite another when we're talking about a fairly major commuter line serving London at one end and Birmingham at the other.
if it's going to drop DMUs by 2040 the government would need to commit to electrifying it as far as Snow Hill pretty soon.
In 17 years? Will they heck. Plenty of vehicles far older than that in London, todays cars will be running in 2045.
Not yet you don't. When it's diesel train vs. electric cars and buses, things might be different...
In 2040 the youngest internal combustion car will be 5 years old and the youngest pure internal combustion car will be 10 years old and approaching end of life rapidly.
I don't hold out great hope for the deadline on production of ICE engines to hold.
https://www.autocar.co.uk/car-news/...-energy/average-car-uk-10-years-old-says-acea from the headline (article is paywalled) says the average age of a car is 10 years old.
They've already introduced the London ULEZ to remove one generation of older vehicles, it's highly likely that something similar will remove all ICE only cars and vans within the next 10 years, and hybrids by 2040. And remember my comment was about London, not the rest of the country.
It's possible that hydrogen will become the favoured fuel for lorries. With battery power for lighter vehicles. Or massive taxes on diesel vehicles, so that produce gets transferred onto smaller electric ones for the last few miles within London.
172s and 185s will likely remain by that time.
If GWR get hold of the ex-TfW 158s they can see off some 165s to send to Chiltern between a fleet replacement, which is some years off and depends on any plans (or lack of) for electrification.
Ironically, the 165s had at least passive provision to be converted to electric units within their lifetime (or that is at least what NSE claimed when they were first introduced).