I tried M4L a year ago, mostly for access to the API for making modules to assist with live performance - things to set, reset and modulate devices but more importantly the mixer.
It didn't work back then - the communication between the patch and the API seemed unreliable, possibly subject to some kind of bandwidth restriction. There seemed to be crosstalk between, for example, line objects talking to different id numbers at the same time.
M4L talking to the API a lot - eg LFOs on 8 sends at a time, caused frequent crashes in the development stage i.e. when the Max window and the Live window were both open. It was wildly frustrating and support were unable to help. I don't blame them as my patch was massive and, shall we say, rather organic - although ultimately correct layout-wise
I got quite a long way with patches but gave up in the end as good old fashioned MIDI loopback did the job better, more simply, with less overhead and more programmability.
I recently thought I would give it another go and have found everything much more stable, and some nice new workflow assists in the new Max, but ultimately access to the API is still pretty hard work. talking to the mixer using line objects and live.object to control smooth parameter changes is still erratic, in fact inconsistent - which surely is the worst of all worlds? the impression is still buggy, no, more clunky - like the programmes are actually quite hacked together and not properly integrated.
a small example - you can send a full scale deflection signal to an object in the API and it does not go to full scale, it stops a little bit short. grab it wit the mouse and you can move it right round.
how is this a correct implementation? how can that be a marketable standard of product? As something fun, but sometimes frustrating, for coders (like me) to play around with - maybe, but I wouldn't perform live with a M4L device. I am sure many do though
So yeah, some sorting our of the API access would be cool.
I was also very disappointed to see the range of Live-specific devices people have made after 12 months. Hardly the vast deluge of quality amxds that one, and indeed Ableton in the M4L release video, expected. Some nice stuff for sure and respect due, but not what I was expecting to come back to. A sad indictment of the Max and Live API documentation i.m.ho. . Although I note some improvements over the original set, still some significant errors, eg duplication in the same html page, in there. I run a company and know what produces this kind of documentation error - time and budgetary restraints limiting quality control - it's not that they don't want to make it better, they just don't have the resources.
My own opinionated view

is that Ableton might have done better investing money in a younger sister program, one that is easier to learn, and perhaps to programme, and grown together with it, rather than trying to get already-mature Max to work with Live. If they could have got Outsim's Synthmaker, for example, ported to Mac as well as PC, that might have yielded more user-friendly results in the long term. I know it lacks the Jitter type stuff etc just now but who knows?