OK, on the face of it one of the most impractical ideas I've seen, even on Speculative Ideas - *but* there is a possible variation I can imagine working - eventually.
No, there's no real practical way you could use this system to open/close doors.
But let's suppose we are at a point in the future where all tickets are machine readable - from a short distance, say 1 metre, *without presenting them*, they are RFID+ tickets in a wallet or NFC+ mobile or future equivalent. And all trains have full CCTV coverage with plenty of computing power to back it up. (+ indicates slightly increased range)
It *is* just about conceivable that you could have a system where as each person boards their ticket is checked automatically, invalid tickets are noted and the CCTV links with this and if the ticket is invalid or unreadable they are tracked to their seat or standing position. The guard is then informed (e.g.) 'all tickets valid, no checks required' or 'this person (insert photo from CCTV) in seat A34 has an unreadable or invalid ticket'. So ticket checks are minimised and manual checks only required for a directed handful of people. On DOO trains staff at a destination station could be alerted by facial recognition systems on the station that a particular person needs a manual check.
Of course, if you registered your face and bank account you wouldn't even need to have any sort of e-ticket, your face would be your ticket and you would be charged the appropriate fare automatically. And if everyone had to do this, there would be no need for tickets as such or anything to read them. It could all be done via CCTV and facial recognition.
I know this may sound a bit fanciful and very expensive - but facial recognition and tracking is being used already for many purposes, and Amazon *already* has stores where you can just walk around, pick up whatever you like, walk out with it and be billed automatically. This is nearly the same thing. Facial recognition is also used at some airports for fast track security clearance.
I'm also pretty sure China is getting very close to this sort of setup already.
IMPORTANT NOTE: I'm *not* saying this is a *good* thing, in fact it could be very, very bad for freedom and privacy. I'm just saying this is the sort of thing that could technically be made to work without delaying boarding, and would potentially be very convenient if you ignore the privacy and freedom aspects.
Also note that I am an IT person (very recently retired) and I do read extensively about this subject, so I do have some sort of idea about what is possible.