From your article link:
"popular phones that have received an update to Android 8.0 Oreo, but currently lack Treble support:"
Samsung Galaxy 8's (S8/+)
I liken it to the transition to EFI/UEFI - EFI 1.0 came out in 2005 and was 32-bit along with other features. UEFI 2.0 was 2008 but wasn't fully UEFI 2.1 compliant but was 64-bit finally.
The device tree that Treble uses is I always thought baked into the core boot ROM and likely cannot be altered. Just like rolling back to pre-8.0.0 won't be allowed.
So you can run 8.0, and not have Project Treble. But what that "means" is beyond me
Funnily enough I sold my Mate 9 to get the S8+, looks like I should have hung onto it now to play with!