Since I bought Live in 2005, I've used it for EVERYTHING. I use it for writing, for editing, for performance, and as a controller (often all at once). The ONLY shortcoming I've seen so far is that MIDI clips (let's call them files, for now) don't read the information written into them. They read the MIDI notes, and envelopes attached but NOT program changes.
Live sets a single program change per clip / file, and that's all you get. To do multiple program changes over the course of one performance, I'm forced to use the ARRANGEMENT view - as they trigger in a linear fashion.
What I and many users would like is to be able to draw multiple program changes into one clip / file. Mainly, for cleanliness. I have moved onto using the SESSION view for performances, because it's clean - the follow actions are king, and it's really really easy to expand / subtract a live show. I can add to it easily, etc..unlike in ARRANGEMENT view...if I have 15 songs in one performance, that begins to get messy on the screen - and hard to manage.
Most MIDI sequencing/editing software (even ProTools) lets you add program changes into one clip/file - and they read....Though I'm loyal to LIVE for life, and am not backsliding to any other DAW.
I think this can be as simple as adding an option to draw PC values into an envelope, just the same as any other control message (volume, pan, express, etc). The values can be represented between 1-128 just like you have, and visually by "Nodes" (or whatever you guys call the little circles that go on an envelope).