Programming Audio Tools. Features I Should Look Out For?

I am programming a very simple audio creation tool for the game I am working on (and probably subsequent games I will be working on). I am trying to get a good list of features to implement and to design the program. What features should I put in this that are not on my list. Right now, here is my non-exhaustive list:
- Sample Sequencer
- Sample Creator
- Ability To Save As Sequence For Modular Sound Components
- Ability To "Draw" With The Mouse Sequences of Samples
- Workspace GUI
- Ability To Save Projects
- Ability To Export Project As .ogg (audio format of my game, or so I plan)
- "What You Hear Is What You Get"; Listen As You Are Creating
- Ability To Mix Sequences
- Ability To Organize Sequences On A Timeline

I am asking this in the audio category, not programming, because I am not looking (right now, at least) for programming advice, but for the advice of people who use audio tools and create audio content for games. If it was unclear, a sequence is a sequence of samples, like a sound effect, and can last any length, be it one second or one minute. Please ask if you are uncertain of any of these, and please give me your advice.

EDIT: Here is an image of the GUI I slapped together in MS Paint: http://i.imgur.com/vw3Jf.png