Anderton
FWIW I too have requested a "drum machine mode" for MIDI loop recording. I would want it to work like Sound on Sound works now, except that the notes from previous passes would be visible and available for editing. That to me is far more important than automatic MIDI merging, which if it existed, I would likely disable.
I've also asked for real-time entry into the Step Sequencer. Of course you can do this from a keyboard in step time, but not in real time.
This is the most basic of functions that every hardware drum machine or sequencer has always done. I think most of us a certain age started on hardware, well before computers became the new standard. Lets change the mindset for a moment. When you record a pattern in a HW drum machine, which is obviously loop recording... each note is added into the same pattern, whereas- you're overdubbing into the same performance. You'll be hard pressed to find a current major DAW or even smaller scale DAW's, that doesn't have this capability. Many offer options for both, clip takes and midi-overdubbing!
The key word here is: Option! No one is speaking of getting rid of anyone's beloved clip stacking. The main purpose for this feature is drum programming. If I record 10 different elements, I don't won't 10 separate parts stacked on one another when some parts are merely added notes to the same part, where I thought of something to add- that didn't come to mind at first. If you're doing EDM or other styles where drum parts can be repetitious, you must bounce to clips if you want your midi clip to be a groove clip! Also, stacked clips can easily be moved out of place if not careful. It's just a cumbersome way to work when it doesn't have to be that way!