Why not make Runes free?
Rune Pages and their RP costs can stay, but there is literally no reason that new players (or just players in general) should have to grind that much IP just to get to have the same playing field as everyone else. I mean, you can't even buy Runes with RP, so what's the point of all this grinding?
In terms of Runes being free, you wouldn't even have to go to the store in order to buy them; you'd just be able to choose what Runes you want. From that, Rune tiers would be straight up removed; only what we have now as Tier III runes would remain. This would also be a good starting point for whatever changes Riot wants to make for runes in the future.
Getting more champions, masteries and getting to ranked are enough of a motivation to climb to level 30. Just make Runes free and we're all good.