That being said, I did not originally mean to post this now (I accidentally hit the post button) because I was going to wait until after the replay night event (http://us.battle.net/sc2/en/forum/topic/7764347062?page=1) to gather more feedback -- so expect to see more additions to this post then!
Watch with party by default: If you are in a party and you double-click a replay file, it will load it solo rather then sending invites to party members and creating a lobby for shared replay viewing.
Allow Transferring Host: I would love it if you could transfer control of the replay to another player while in the middle of watching the replay. It has annoyed me to be locked as the host on several occasions -- its useful if the host has to go AFK for a bit, or if another player wants to rewind to a certain part of the replay and can't remember the time stamp to tell the host.
Follow Spectator Cameras: There is the option to follow the camera of the players in the replay, but it would be a big improvement to be able to follow the camera(s) of anyone who is watching the replay with you. When you want to show someone the action or bring attention to something in specific, it would be much easier to simply say "Hey, follow my camera and I'll show you something cool" instead of trying to use pings, pause the game, and yell at them in the chat to come look at it before they miss it and you have to rewind again.
Replay Folder for Downloaded Replays: Quite simple: A folder where replays will be stored when a friend invites you to view a replay you don't have. Options to choose if these are automatically saved or not would be nice.
Replay Paused Text: Right now, when the host pauses the replay there is only an audio notification. If you don't have sound or were away when the replay was paused, it would be nice if a text message "Hostname has paused the replay" appeared for the duration of the pause.
Allow Referees: Right now, all spare players are made observers when you load from a replay. Please allow us to select them as referee\observers in the lobby before loading the replay.
Fast Forward: Running at x8 can be quite laggy and still not very fast. I would love it if you could fast forward the replay just like the "recover replay" system works. It doesn't render the graphics so it can fast-forward through the replay at greater speed, without lag.
Drawing Feature: Similar to the "weather screen" tournaments like MLG are using. Watch "Axslav's Rules of Engagement" on the MLG stream for an example. The reasoning for this feature is simply to give you more tools to explain concepts to your fellow spectators. Pings are very limited in utility, and only show up on the mini-map -- drawing on-screen would allow you to circle units, draw arrows to show where you should have moved your army, and so on.
Public Replay List: On the replay tab, there should be an "Open Replay List" like the custom games section. You should be able to open a replay lobby to the public, so anyone can watch.
Show in Match History: I was kind of disappointed that if you load from a replay, the game doesn't appear on your match history. Obviously it would be necessary to make alterations to the score screen and match history so that it would display as [Loaded from replay] to avoid confusion.
Start Recovered Replay Paused: Taking control of a regular replay is fine: You can prepare yourselves as long as you want before clicking "Take Control." However, if you recover a replay it counts to three and throws you in. Instead, please bring up a pause screen with a "start" button so players can begin the game when they are ready to.
Other Preparation Settings: Sometimes the control groups from the players are not set up how either of the loading player wants them -- it would be nice (for both "recover" and "take control") to allow players to set up control groups before starting play.
Allow AI. Pretty please! Allow us to load an AI player into a player slot when using "take control" -- I understand that the AI wouldn't be able to competently take over, but it would at least make the enemy units keep attacking. It would have limited use, yes, but there are cases when I want to do so.
Display name of Host when players load a replay. I've been doing this thing called Replay Wars (http://us.battle.net/sc2/en/forum/topic/7764876602?page=1) where the losing player gets to load. It would be quite useful if it told you who the player initiating the load was, so you could tell who lost the previous time. I have one replay with 7 different load points, and it would be very helpful in keeping score for Replay Wars if it told you who loaded.
Tabs on Replay Timeline that mark where the replay has been previously loaded. It would make finding the load points on a replay much easier.
Clan Tags don't appear on the message indicating what players loaded into the game.
Many people I tried this feature with expected you to be able to go back to the replay file after you took control. I expect this is technically infeasible, but if its not it would be a superb feature: Then you could make a quick demonstration from within the game itself, and then go back to watching the original replay without having to reload the entire replay.
Thats it for now. Thanks for reading!