Fast forward to 2020, I have the same question :rolleyes:
I am currently researching the subject and decided to post my findings so far:
1. It seems like Apex are planning to introduce the barrel in question in the "near future" (see comments at Apex Releases Threaded Barrel for 9mm M&P M2.0...
Same here but I am not concerned about the gun being used.
I can't be 100% sure the "hood" had no signs when I handled the gun in the shop but I think I would have noticed.
I've noticed the signs only a couple days later and only after initial deep cleanup.
My theory is that the wear on "hood"...