Shimano doesn't make bikes. They make components. What advantage to "not wanting people dicking with their equipment" is there? They technically would want people using their existing components in every way possible that makes them money (i.e. folks buying it to put on their builds)

The hard fact is that that the vast majority of large builders (The large MTB manufacturing brands) are not building 1xN systems right now. Most production mountain bikes and are triples or compact doubles and short-cage derailleur applications off-road are just not that popular at the moment. There just isn't money catering to tiny markets at first. Shimano might eventually get around to eventually making a fringe product for a fringe market (perhaps for the downhill segment, or CX) but until then if you want one of these new clutch-systems you are going to have to buy the higher-end MTB shadow derailleurs they come on. Right now those are all long-cage. Maybe, probably, it will begin to trickle down to other product lines. When it gets to Acera...