I gave it a quick check this morning with the Android M developer preview on the Nexus 6, but didn't notice any improvement for midi. Timing and Latency are exactly the same (at least with a regular micro usb connector).http://arstechnica.com/gadgets/2015/05/android-m-embraces-usb-type-c-midi-devices/
After a closer look to the api docs, it appears to be a new system service, the "MIDI_SERVICE", which will actually deliver the complete MIDI connectivity and integration.
The API features include:
Enumeration of currently available devices. Information includes name, vendor, capabilities, etc.
Provide notification when MIDI devices are plugged in or unplugged.
Support efficient transmission of single or multiple short 1-3 byte MIDI messages.
Support transmission of arbitrary length data for SysEx, etc.
Timestamps to avoid jitter.
Support direction connection or “patching” of devices for lower latency.
It'll support sending messages from and to external devices as well as between apps.
That sounds indeed like an excellent and long awaited addition.
So far so good, but back to reality:
Since even Android 5 is by far not rolled out to all devices (at the moment around 20%, 45% still running on kitkat), it may take a very long time until these improvements become reality. I'll of course integrate it in the G-Stomper MIDI driver, ... as soon as the official API is available.