I am heavier and haven't gotten over 10,000km on a Marathon Plus tire but typically get close. However, agree they last longer than other tires that I have used. Photo below of an old tire I had worn until the blue was showing, the new replacement tire and the Amazon delivery box that I had ordered the new tire to arrive in Liberal KS for me to pick up...
You're a better man than I am, Gunga Din.
I would have been panicked if my tires wore that much, not to mention the loss of traction...