1) Parsons did NOT leave the group. Please don't let LRC trolls get to you so easily...
2) There is ONE workout on Strava that I've seen do a Tinman athlete do a double workout recently. It's their long-distance/marathon specialist Reed Fischer, who did the workout you prescribed on 1/12:
https://www.strava.com/activities/4609854057
(AM Tempo)
https://www.strava.com/activities/4611717009
(PM 600s and 150s)
This doesn't really mean anything.
Tinman is a scientist. All he has ever done, and based his own coaching philosophy (which isn't really more than a combination of 4332 other philosophies out there), was to look - what have other great coaches like Lydiard, Stampfl, Bowerman, etc. done in the past? What have swimming coaches or lactate experts like Olbrecht done in the past? What worked for myself/other runners and what didn't work?
So it is not out of the question that he "discovered" double workout days recently, and is starting to prescribe them to some of his elite athletes who he thinks would be able to handle this type of training. His philosophy was always - hard days hard (but not "run-to-the-well hard"), easy days very easy. Double workout days fit well into this simple philosophy so why not prescribe his marathon specialist a double workout?
Does it mean he would prescribe it to his 15/16/17/20/25 min 5k hobby joggers? Does it mean he would prescribe it to his upcoming 50-60/65 mpw HS kids? No, he probably isn't going to drastically change his training system.
And I think that's the perfect way to use double workouts - use them on highly fit, elite runners to reach the next level. I still think it would be a mistake for the average 17 min 5k 50mpw LRC guy to start doing double workouts twice a week, but it might help his elite runners to get just a few seconds faster which will help them in their preparation for trials and Tokyo/Olympics.