Notch made an note a few years back that he would not want Minecraft on Steam, because of Valve's weird rules. "Don't get me wrong, Steam is an awesome platform, but not for Minecraft" -Notch.

i dont think it should be added to steam.

also Mojang never wanted Minecraft to be on Steam

Steam makes it very hard to mod/take files from games and minecraft is very flexable compare to some games.
All games on steam are compiled into weird file types that you would need a special file converter tool to undo.
Lets say you wanted to make a texture pack, you may have to convert all .png files to .tga or something like that just so the steam version could read it.
Besides, minecraft in my opinion is too profitable to just give to steam.
Minecraft doesn't need to let steam take 30% income just so it can be advertised, and as far as I know steam doesn't have much it can offer to a successful game like minecraft.

Steam is a great place to advertise a game and an easy way to get it to the people that want to play it. Steam also charges a hefty percent of the profits for every game sold (I've heard it could be as high as 30%). I see no reason why Microsoft will sacrifice profits to gain something they don't really need.

I highly doubt that will happen, but anything is possible. It would be helpful for noobs though, for installing mods and such.