Frankly my expectations for the mod API are pretty low, if they actually do listen to the community feedback. There's some truly handicapped design choices being widely hailed as great ideas floating around on the MCAPI tracker. Not to mention that Grumm was somehow convinced that server-side sound management was not only a great idea, but it is apparently also impossible for the client to have any idea what sounds to play on its own (for instance, based on what you're walking on, your armor, whether you're sprinting or not, underwater, etc... the client, according to Grumm, cannot access this data at all) - that's nothing against the API itself, but it certainly doesn't do anything great for my faith in the people developing it.
I mean, it's the Bukkit guys developing it - yes, they do know what they're doing, but the "no clientside code" approach to modding is literally crippling in terms of available polish and functionality. Clientside effects can do wonders for how entertaining something is to play around with, and a lack of them can literally be the death of an idea. Take, for instance, something that implemented Dishonored's Blink ability on Enderpearls - that nice cursor showing where you land, without clientside code, would be either visible to everyone (annoying as hell) or not visible at all - thus removing the actual feedback as to where you land and making it nigh impossible to use. The little screen bounce effect also does a lot for how satisfying blinking around is. Sure, you could make it functional, but it would be unintuitive and not all that cool without the clientside effects.
Another thing they're talking about is moving clientside prediction off entirely so serverside events can be processed based on key input. Now, for a game with fast, efficient netcode, this is already still a bad idea - 100ms on input (or audio!) is utterly jarring, and when my laptop is speaking to my desktop over wireless Minecraft pulls a mysterious 150-180ms average ping (despite an actual ping packet passing in <1ms). If the client essentially did no processing and only sent your input to the server, the game would be literally unplayable - not just troublesome but actually so unresponsive as to be considered non-functional - to most remote servers, for basically any player. I seriously hope there's a good dose of reality checks before anything is implemented here.