My friend, I know a lot of players who have, like myself, unlocked all the champions in the game. (I have played over 3000 normal games and a whole lot of rankeds and earned around 500k IP since I have started to play) I have 10 rune pages and almost all the top tier runes. It's been a long time since I have spent IP on something that I really wanted. For exemple, I had enough IP to buy 2 summoner name changes (13 900 IP each). And I'm not even among the top 25 000 players who have played to most.
You can also see a lot of streamers who have played a lot and unlocked pretty much everything that is affordable through IP and that are now stacking them to amounts as high as 60k IP.
So yeah, I think the idea is good, but maybe the approximated number is too high. Something around 20k to 30k IP for a normal skin would not hurt riot's RP sales, I think, while it would make some veterant players like me much happy to really get something off of their IP.