Rules & Regulations on crash protection mean that we can't just order Siemens to fabricate gangway cabs to be affixed instead. Besides, they've already taken down the jigs for them in favour of the Desiro City Disastro Sh**ty units instead.
(my opinion of them might change if the Dft decided not to go for ironing boards)
That's not to say that Bombardier's Aventras aren't cheap - they're built well, but just plagued with software issues that *finally* appear to have been resolved. CAF meanwhile...you need only look at the farce of the 397s and Mk5a coaches to think of a derogatory acronym.
Again, it wouldn't usually seem right, but as mentioned, the ARL in Bangkok basically already operates Class 360/2s, and desperately needs more capacity, so it's a no-brainer IMHO.
This mini-conversation on Class 360/2 Retention is wildly off the topic of refurbishment of Class 350/1 Refurbishment though.