Access is through Max for Live, which is a dataflow language "programmed" by joining little object blocks to other object blocks - like Scratch. There's unofficial Python support, but it's poorly documented.
Many things are possible, but many other things aren't possible - even though they're available on Push, so obviously the hooks are there.
It would make me unbelievably happy if Ableton opened up the LOM and included a properly documented hook for absolutely every important feature - preferably one that could be used from any language, maybe via OSC, rather than M4L.
To be fair Live at least has a LOM, while other sequencers/DAWs don't. So that's a plus. But it's still a shame it isn't more complete - because that would make all kinds of cool things possible.