If they were that worried about losing money on rune page purchases (which they really shouldn't be, we only really need one mastery page, but we still use all 20), why couldn't they just make the runes themselves purchasable through RP. I imagine that would more than make up for any losses on page sales. I for one would love to not have to spend almost as much IP as a fully priced champion just to fill out the quints on some of my pages. And besides, since the pages themselves are purchasable with IP, they clearly aren't that worried about losing too much money on them.
Being able to edit runes in champ select can only increase the quality of the game. And it might actually get some people to start caring about them a little more. As it stands now, even with 20, you just kind of have to hope for the best when making them. Unless you're dedicating them all to one role, and only play a few champs in that role, you won't have even close to the number of pages needed to cover all the possibilities. And so a lot of players just make two super generic pages and leave it at that. We can easily fix that.