Legacy champions (Pre-reworked champions being playable)

Inherently some champions give off the feel that after reworks, they are completely different because of the vast differences in the kits. When Riot approaches these champions, they always claim they are looking more towards the thematic of that champion instead of it's original kit..

So my question is: How hard would it be for Riot to implement 'legacy' champions. Simply put, the old champions from when they were reworked. Cant imagine it can be that hard?