I'm bumping this because I still want it.
Propellerhead, for a good example check out the Yamaha PSR-510 keyboard's implementation. It makes use of a "step" button which is used to create rests, held notes, and legato notes of any length. It even supports chords, since it doesn't advance the playhead until "all keys up" or you hit the step key. In Reason I guess the "step" key/button would be used to enter step-record mode, and the escape key could be "go back to normal mode".
Last edited by rogerlevy; 2013-06-10 at 20:32.