So to summarise - the MML HST situation faces a choice between 3 unsatisfactory solutions, which I have decided to nickname Dodge, Bodge and Fudge*
- dodge the 2020 deadline by a derogation from regulations
- bodge together a Franken-HST with Mk4s that will be even slower (it'll be more like a 2+9 with Mk3), and do a rush-job on up to 22 stations
- fudge the regulations with (perhaps) a single compliant Mk3 carriage per set
Perhaps there's a 4th option we haven't thought of, involving unicorns and slogans on the side of a bus, but I'm not even sure *that lot* are sufficiently delusional.
So, I'd comment that perhaps we're missing the point. Instead of debating the pros and cons of these solutions, we should be hopping mad that this situation has come to pass. To me, it's a lovely example of the failure of the industry structure to be accountable (by the way, I'm not advocating public ownership, because IMO it's DfT that's royally mucked everything up).
A thought experiment: Can you imagine the pyrotechnic outbursts and sackings at the HQ of IAG, if British Airways had been given 10 years notice that it wouldn't be able to fly 747s from Heathrow, were now less than 2 years from that deadline, and the senior execs had no workable plan?
OK, rant over. Where's my beer?
To make a token gesture at being on-topic - one reason EMT's HST power cars probably won't get a 2nd life with XC or some other 2nd tier operator is that this small fleet have different engines so are a little non-standard.