Woot they're adding replays to LoL! ...eventually!
One problem with replays in most video games is that they don't store literally all the information of a game because the file would essentially have to either be a straight-up video or as big as the entire game itself; otherwise the info in the replay doesn't produce an accurate recreation when run through a game with a different version. For example, if the data is "Dr. Mundo attacks Anivia here and now", and the replay method saves disk space by not recording damage values, then the output is different if Dr. Mundo's base attack damage changes. This has a butterfly effect that makes even minor patches render replays entirely useless.
RIOT has just released an updated patcher that they claim will alleviate this problem and allow replays to work even after the game is patched. This means that they'll finally be able to roll out a replay feature. Here's hoping we get it soon!