Why wouldn't this be possible? The term "on the fly" gets thrown around so much, though, so maybe I just don't understand what you are asking. Why would anyone need to stop the playback of a drum machine just to switch patterns?
I'm curious how quick live sampling of the inputs could be. The quickest workflow I've seen yet is the OT's pickup machines, but that style doesn't seem possible on the DT. But then, it's not designed to be a looping type sampler, I think.
I'm going to have to wait a bit, but I definitely want this box even if they release an OT2 in a year or so.