Who would have thought that the Koran teaches God promised Moses that the Land of Canaan belongs to the Israelites?
Re: Is 17:104 a Prophecy for the Land of Israel?
There does not appear to be a prophecy in 17:104 if read in the Arabic and compared with 17:7. This may be a problem with translations. Let me show you.
First, there is no 'second' in the Arabic as is commonly translated (i.e. when the 'second' of the warnings...). Also note carefully the Arabic in bold and in the illustration. I will translate it more literally from the Arabic for you to make the point.
"If you do good, you do good for yourselves and if you do evil, (you did it) against yourselves. So when the promise of the last came (Arabic: Fa-idha jaa wa'du l-akhirat), (we permitted your enemies) to disfigure your faces, and to enter your Masjid as they had entered it (the ) first time, and to destroy what they had conquered (with destruction)"
Note the phrase "Fa-idha jaa wa'du l-akhirat" (So when the promise of the last). In the above verse, it is clearly referring to a past event most likely a reference to the destruction of the Temple in AD70 by the Romans.
What is important to note is that the same phrase is used in 17:104
"And We said thereafter to the Children of Israel, "Dwell in the land (of promise)": So when the promise of the last of the warnings came (Arabic: Fa-idha jaa wa'du l-akhirat), We gathered you together in a mingled crowd"
They are both past events with the identical Arabic used. I am not sure why so many commentators, despite the Arabic, translate the latter verse 17:104 differently and understand the 'akhirat' here as hereafter but not in 17:7. The only one that I know who translates it with my understanding is Yusuf Ali.
I feel both verses deal with the events of AD70 and 17:104 is not necessarily a prophecy about a future event.
Finally, 5:21 has a context. Prophet Moses spoke directly with his people and informed them that this particular land was assigned for them. Now the question is whether this is strictly his people or the Children of Israel forever. Note the term 'Bani Israel' is not used in 5:21, only 'ya'qawmi' (my people / community). Then if you read on it was banned to them for forty years because of their transgression (5:26). So a particular generation seems to have been punished. This also lends strength to the argument that this land was promised to a certain people with Prophet Moses. Also, remember that the other Israelites inherited the Eastern lands (7:137) as not all the Israelites left with Prophet Moses.
EXODUS OF PROPHET MOSES'S (pbuh) PEOPLE
As I don't understand the verses the way you have intimated, therefore I cannot answer your pointed question. However, I will say that no one has a right to usurp another's land. Also, I don't necessarily see any Biblical right to land categorically supported by the Quran. 5:21 has a context. 17:104 and 17:7 don't seem to be translated consistently given the Arabic. However, in persecution the Quran clearly encourages 'Hijrat' (migration). There are many verses where God says His earth is spacious. (29:56; 39:10).
There is a strong inference in the Quran that those persecuted will be asked:
"Lo! as for those whom the angels take (in death) while they wrong themselves, (the angels) will ask: In what were you engaged? They will say: We were oppressed in the land. (The angels) will say: Was not God's earth spacious that you could have migrated therein? As for such, their habitation will be hell, an evil journey's end"
"Except the feeble among men, and the women, and the children, who are unable to devise a plan and are not shown a way"
So this is another perspective to consider. After all the Prophet also was forced to migrate under persecution.
In the end, only God knows best.
Your brother ...