Well, it would be considered a baritone guitar, in the same way that an regular electric bass is considered a bass guitar.
It's really an instrument in it's own regard, but definitely have more in common with a regular 6 string guitar, than a bass guitar, from a design perspective.
A bass in baritone tuning is considered a tenor bass guitar.
This might look like contradictory, but mind this it here is referring to a tenor guitar (4 string short scale guitar) in bass tuning, not tenor as the frequency range.
A baritone guitar works best if you play it considering neither a regular 6 string guitar or a bass, but an instrument in its own regard, that requires its own unique playing style, sort of a crossover between traditional bass and traditional guitar playing style.
A Bass VI is also neither a regular guitar, bass guitar or baritone guitar, but again an instrument in its own regard.
I suppose you could call it a long scaled guitar in a bass tuning, or a short scaled 6 string bass with narrow guitar like string spacing, but that would be missing the point of the instrument.
It can sort of be played like a bass, and it can sort of like being played as a guitar, but again really works best when you adjust your playing style to accommodate its unique design.
In any case it doesn't really matter how we categorize instruments, what matters is the we adjust our playing style to actually fit the instrument in question, both from a design and frequency range perspective.