I'm aware this is the most anti-ableton/cycling mindset suggestion I could make but hey... take it as food for thought:
Understandably, M4L uses the instrument/audio effect/midi effect plugin paradigm as a useful limitation... On the other hand Max's strength is that its "anything in / anything out."
I really wish there was some way to transcend the audio plugin I/O paradigm of M4L. I've seen a lot of requests, for example, of midi side chaining to audio plugins, multichannel MIDI input, and multichannel audio.
I'd really like to be able to easily and intuitively combine multiple inputs and outputs without resorting to awkward routings, porting around stuff with send/receive and even super unreliable UDP objects.
Pie in the sky solutions:
1) In addition to plugins, Max inside clips (possibly with custom jsui editors?)
2) Perhaps a design sensibility nightmare, somewhere in an Ableton set, we should be able to load a master max patch that can handle all the I/O that ableton has access to with the ability to send these signals and messages back and forth between track inputs, plugins and this patch.
3) Max inside of live is a bit of open endedness inside a highly structured environment. I'd much rather have a bunch of structured ableton elements inside the open ended Max environment. Ableton's strong suits that max lacks are the traditional GUI elements and algorithms. An audio DAW, the MIDI editor, clock syncing, the session view channel strip, also the ability to insert and remove stuff from the signal chain without interrupting audio, also automatic BPM and onset detection of audio.