1. Completely free key assignments. There are so many features in Live that I don't use that are hard-wired to keyboard shortcuts that I would like to re-assign. A lookup table is already used for some elements, so why not just take it all the way? A simple reset would allow you to start from scratch if you make a mess. And allow export so users can share theirs.
2. Same deal for color. Implemented the same way. Just click a "colors mode" button and select colors for each element to taste. Import and export as well. Or at least an obvious file that users could share.
3. MIDI file output. As of now, you can only create MIDI files from clips so it's a real hassle to export an entire song if you want to collaborate with someone using another DAW, or a studio using Pro Tools, or mix with another program that's better at it. Just about every DAW in existence does this.
4. Just a couple more options for the audio export, such as pre-fader, pre-FX, etc. in case you want to export the audio stems to another program. Same reason as above.
5. Hiding the clip launcher (which I personally never use). I've seen this suggested as Mixer mode. I like the idea, and it shouldn't be too hard, though if the whole deal was programmed stupidly it might. I have a feeling it isn't. There's a hidden tweak for showing the inserts so that's some evidence that it should be easy right there.
6. Eliminate the export and preferences dialogs and move them to the right-side pane that contains the file manager. And of course, add a shortcut to view that pane. I have a selfish reason for this which is that I zoom the interface quite a bit, and the preferences don't scale. I literally have to take off my glasses to read the thing.
Yes, most of these pertain to arrangement usage. I have little knowledge of live performance using the program, but I'm sure there could be tweaks for that as well. Have at it. And of course, I'd like to hear what you think.