Chromas being sold for IP is something that did/will happen. The plan with those is that twice a year they'll be available for IP, and return to RP in between those sales. There was one such sale already, and we're probably due for another one soon-ish but theres no set dates so one would have to watch the news. Buying every single chroma available for ip costs alot more than 30k ip though, so if chromas interest you it's worth it to keep saving up.
Theres occasional icons for ip (albeit usually not for much) and other event things that sometimes use ip, but eventually you are just going to have everything, and they can't make too much available for ip because of all the people on the other end of the spectrum who wish there was more ways to get ip since they can't afford all the runes/champs they want, much less all of them.
When/if they rework runes it'll be interesting to see what happens with existing runes, and if whatever replaces them might open up further ip spending opportunities, but theres not really any info about that beyond that they'd like to rework runes at some point.
