Patch 2.0.10 to improve replay experience

?The next patch to hit StarCraft 2 will apparently be big enough to force older replays to have to be viewed on previous versions of the client. 

While no information on what the patch will consist of is give, we know as much that one of the features will be the option to jump forward into a replay without having to buffer first.

Because the patch will be a massive one, replays recorded before its release will have to be loaded on previous versions of the game. Blizzard clarify that said replays will still be watchable and expain:
 

StarCraft II has always automatically loaded replays in the appropriate version of the game behind the scenes, so you can continue to watch your old replays just like you always have. Something you may not know is: whenStarCraft II loads a replay in an older version of the game, it has to disconnect from Battle.net. This means that some of the new, advanced replay features that were added in Heart of the Swarm aren’t available when watching replays that were created in 2.0.9 and earlier.

Simply put, after patch 2.0.10, you won't be able to watch old replays with your friends, and you won't be able to recover multiplayer games from replays created in 2.0.9 and earlier. This was also the case when Heart of the Swarm was released -- watching replays with others and recovering games only worked with replays created in 2.0.4 and later.

Source: Battle.net