Don't worry folks it is strictly optional:

I actually called this extra peripheral a couple of days ago in a conversation I was having with Naz on Steam.  My gut feeling at the time was that it was going to allow the importing of songs from professional editing software.  There have been rumors that some big names who have already had a chance to get hands on with the game expressed an interest in using it as an anonymous feedback platform for their own songwriting.  I think a keyboard is actually a likely way to implement it but I'm not sold on it yet.  Again those are rumors, but I did call the peripheral.

Whatever it is, I think the fact that they are releasing a peripheral specifically around the music creation system should give an indication as to how much effort they are putting into make it a legit way to create music.

Source

And for those who don't care too much about how songs are going to be created in the editor there is news that they are  implementing a ranking system inspired by the popular CoD4 rank/perk system.  This should add a whole new dimension of addiction to the game =P

Keyboard would be spectacular although I think they have to pay Konami since they probably own the patents for that too.

A midi box would be nice too if you don't want to have that big drumset lying around just to use midi.

They will definitely need another input source for controlling the studio. Hopefully it will not cost more and come separately.

Cool I keyboard would be awesome.

A keyboard would be much appreciated on my part. It would motivate my friend to chip in on the game, since he plays a keyboard and loves writing music. Activision is making this all the more tempting for me to purchase later in the year.

^^Its not quite confirmed as a keyboard yet but it's definitely a good option.

Am I the only one hoping for a keytar?

Like this?

Thats cool. I am kinda worried, when seeing the demo though, that the in-game option would be like a limited version of the Apple software from school. (I forget the name of it). I really was hoping to do more like be able to download a song. mix or edit it. input corresponding note/play commands then post it for others to play. I guess we shall see if something like that will be possible or not (might have copyright/BS law problems with that idea). At any rate I'm sure they will do what they can.