I like the idea, but since it sticks out it would be all too easy to catch it on something in a crash scenario ripping it out of the hole, spilling oil everywhere, probably irreparably damaging the threads or possibly even knocking a chunk out of your casting too.
Plus in my case it would never be allowed to pass tech at the race track...
If the drain plug was hidden by a bunch of stuff you'd have to remove to get to it then a drain valve might make sense, but as the 919's drain is hanging out in front of god and everybody it isn't really needed. Wanted maybe, but not needed.
Also, while I haven't seen one on a bike I have seen them on cars, most notably a Honda that needed a motor replacement due to oil starvation from very well aimed rock that opened the valve and dumped the oil until the "time to replace the motor" light came on. An insurance claim and annoying. Dropping 4 quarts of oil right in front of the rear tire, however, open a whole 'nother can of worms.
I've ran one of the Fram drain valve setups on two pickups I've had. I like them because there's no valve. It's a cap you remove and then a hose that has a stem that depresses the valve stem of the "plug". They work great on those.
Like Rob siad, the 919 plug is so easy to get to it's not a real problem when servicing.
"Towards the end of the vid, it looks like she may have had a bafflectomy." - MarylandMike