I know, this might be a little early since the replay function hasn't even presented to the community yet, but I've always hated watching replays of dota games on WC3. 90% of a dota game is boring to watch and i've often missed the other 10% because I wasn't able to stop fast-forwarding fast enough when I tried to skip the lame parts.
When I heard about the K2 engine being able to handle rewinding and jump-to-second-X-of-the-game seekers I was absolutely amazed. Because of this feature, my suggestion might be less of importance, but i'd like to see this implanted though.
Would it be possible to give players the ability to set bookmarks in a replay and add a little description about what exactly the bookmark is referring to?
I'd love to watch a league replay where I simply can click on a small mark over the game progression bar and the games jumps to one of the game highlights.
Also I'd like to be able to set comments in the replay that pop up when the game hits time X and tell the viewer for example, that in 6 seconds there is a really epic gang on the top lane that he shouldn't miss at all.
This could also simply be combined with a bookmark feature or other things like a small button within the pop up window that simply moves your camera to the predestinated location of the forthcoming event.
Might be useless because of the rewinding feature but I'd like to see something like that, though. Feedback is welcome.