My idea doesn't necessarily alter the gameplay of Minecraft, however it would make the game feel more classy, and appear more professional.

Concept|
Well right now the launcher for the game is very plain and relatively choppy. Something the developers of Minecraft should do is do some work on the launcher itself.

Details|
Well, remove the update feed, as when you log in, you automatically realize, "Oh hey, an update!" When it prompts you to Update. Instead, put the update feed on the main Minecraft website, so they if the players truly want to know the details of an update, they can simply go to the site and read the details.
As well as replacing the basic format, moving around the login form, the logo, etc.
Another thing that would be done would be a different background, the grey bricks and dirt are an overused Minecraft cliche.

Implement|
This could probably be implemented very easily, many 3rd party Minecraft programs have already made new launchers for the game, and they are mostly non-professional coders, where-as the Minecraft developers could most likely do this type of change in a short amount of time, and very easily.