Dear brother Joseph,
"There is a strong implication that this was because they had already 'submitted' in purpose to what they believed was from God."
Thanks for the reply. In my view, I think the above is possible also.
Firstly, the whole notion of Abraham thinking God told him to sacrifice (as in slaughter) his son in a dream doesn't make sense according to Quranic principles. Perhaps one could argue that is why he asked his son's opinion, but interestingly he replies "O my father, do what you are commanded. You will find me, God willing, of the patient ones.". If it meant slaughter, it seems odd he would concur and use the word "commanded" - as he seems to automatically deduce it is a command for some reason.
Note the order of what the son replies. According to corpus.quran.com the prefix "sa" is a "FUT – prefixed future particle sa" and patient ones" is an active participle, and these come after he says "do what you are commanded", implying do what you are commanded and God willing you will find me of the patient ones. Obviously, if he is slaughtered him being patient or not does not make sense.
To me, the implication is that the vision was from God. If not, we'd have to assume whatever Abraham dreamt, he thought it was commands from God, or at least, this one was, and so did his son apparently. Seems unusual to me, but possible. They both submit to whatever the dream was about, then it says "We like thus reward the good-doers" - now, if the command was not from God, then the implication of this is if one thinks (in a dream lets say) God is commanding them to do X (even if X is not from God) then this will be rewarded and you can be described as a good-doer. Since when is doing something that goes against Quranic principles (as you admit it would have been) for the sole reason that one happens to think it is from God ever discussed positively in Quran? Never to my knowledge.
Further the word "trial/balau" is always used in Quran as from God.
Having said the above, it is not definitive that is was from God, but there is certainly evidence suggesting it was.
If it meant slaughter, then technically he did not fulfil the vision. He was about to, but did not complete it. But this could be argued against as you have said.
And lastly it says "And We ransomed/exchanged him (son) with/by/for a great sacrifice." which to me, the use of "great" seems odd if it meant an animal replacement for slaughter.
If this is coupled with what I said previously, and the definitive "settled some/of/from (partitive) of my progeny" in 14:37 this implies a clear split between Abraham/Ishmael/Isaac, i.e. they are not all in the same place.
Please note, I am not saying my understanding is solid, but I do consider it reasonable.
Am I therefore correct in understanding from your response brother Wakas that there is no evidence that you know of from any classical source or spoken Arabic language that the word 'dhiba' is used to 'give someone up' for example in a noble cause as a primary proper signification of the Arabic term 'dhiba'?
I have not checked most classical arabic lexicons if the word is used to mean "sacrifice" in a non-slaughter way, or a similar meaning, but I have checked Lane and DofQ and not found such in them. If you have, please let me know.