I am fully aware that there are plenty of threads about this and you gave plenty of answers. Most people simply write that they want it. I will give different argument:
Runes currently add nothing to the game other than reduce accessibility and is a nuisance at top level. Absolute majority of players has and will always have 2 rune pages and only basic runes. So it leaves most players with not a single meaningful choice made, and usually its this - ad rune page and ap rune page.
We all understand that you really really want to make money from runes. But nobody is going to buy them when there are so many champions to buy and basically nobody has ll the champions anyway, don't mind you always releasing new ones. Runes are irrelevant once you have basic ones.
Now imagine what happens if you let people edit runes while in champ select - suddenly runes become something to think about! You could tailor runes according to the enemy and your team compositions and you wouldn't feel cheated actually feel the need to buy runes!
I can't talk about others, but if runes would be changeable in select screen, I would make it my goal to buy all of them. Right now I neither buy them (outside of basics), nor think much about buying rune pages. And yet people with many rune pages have a certain edge.
So my advice is this - don't be blinded by greed and let people change runes in champ select. You will see how people will actually spend more money on runes and you will earn more even.
And remember - runes are not incentive, or luxury - they are necessity. It's' not people who has runes that are rewarded - it's people without them who are punished. Is that your philosophy?