I don't really care that much about 2018 vs. 3.8.x except that it be consistent. When I first started playing FS, I was confused whether 3.6.12 or 2014 was newer. As long as the version numbers are comparable, it's pretty easy to figure out that higher is better/newer. If I had to pick, I'd pick the 3.8.x scheme because it's already compatible with semantic versioning, which has some nice advantages like letting you know at a glance how major of an update a new version is.
You could rename the MVPs 2018.1.0, 2018.2.0, etc. in Knossos, but that would just confuse everyone who already has it figured out.
Honestly, if you're just using Knossos, which everyone who can't figure this out should be, it's not a problem. If you want to play FS2 with upgraded visuals, you just install the MVPs and Knossos will give you the latest ones automatically. If a certain mod requires an older version, Knossos should pretty much take care of that seamlessly.