Why doesn't riot just take the smash Bros solution to reworks and KEEP the old version of heavily or moderately heavily reworked champs alongside the new ones. Lore can be changed to be consistent with new champ version, but keep the old ones in a viable, slightly weak state (48-49% winrates)? Some of those older champ designs we're beloved by mains and some we're even good gameplay design like old sej, Yorick, and galio. Aatrox was hard to balance, yet some people still loved to play him. If kept in a perpetually slightly under buffed state, they could be played when in skilled hands or in the right team comp, etc, without being a balance nightmare for riot, riot could focus energy on moving forward with reworks and new champs, etc. This would be an awesome consolation prize for many players who just want to play the champs they remember and love. Likewise, some players get used to the reworked versions and like them more and will miss them if reverted. This would appease most if not all parties. Which ever version is the primary one (new rework or revert) would get the balance attention and the other would be kept slightly nerfed but as I said, in a viable condition. They could have a distinguished look like a different color or whatever so allies and enemies know which version it is so they know what gameplay to expect
But why did I relate to smash Bros? Because they successfully pull off multiple versions of the same heros so that people can enjoy different versions of the heros they love. I.e, Mario, doctor Mario, Samus, dark Samus, toon link, young link, normal link, zero suit Samus, and shadow fighters like half of the swordsmen, Richter, Simon, etc. I don't see how riot should have much difficulty doing this.