I have been lurking on this thread and I will admit to not having read the last page or so but....having read the thread from the beginning I was terribly excited at taking a train journey with dd in her pram today, all the while with this thread in the back of my mind.
As OP describes, I got on in the wheelchair access carriage and lo and behold on each side was a space for 1-2 prams or 1 wheelchair with two seats. One side was occupied by two women with large suitcases so I parked the pram on the other and me and my travelling companion sat down. Two stops later not one but two families with buggies boarded. Right, this is going to get interesting I though, still with this thread echoing in my head.
First family came on, said nothing to two ladies with suitcases but asked politely if they could fit their pram in. Started making motions to get child out of pram etc. Ladies with bags started to shift their bags and I offered to help them lift the bags into a luggage compartment. Still no one had mentioned anyone moving. Then, as the luggage compartment was further down, the ladies offered to move seats and sit closer to their luggage. By this time the other family had already folded their pram, taken their dc and sat down in another carriage.
On the way back similar scenario. I got the left wheelchair access area and chap with suitcase was on the other side. Another family with pram board. Again, they politely ask if they can fit their pram in, and husband takes dc to go and sit somewhere else while woman sits in spare seat next to man with suitcase to keep and eye on pram. At this point man with suitcase offers to move.
At no point did anyone ask anyone else to move, speculate about anyones disability, no one was rude or made anyone feel uncomfortable, no one had a sense of entitlement to a seat just because they had a pram and the whole situation was sorted out in a few minutes. So see OP, it is possible to travel by train with a pram without resorting to rudeness!