Just a possibility I don’t see discussed on the wiki page.
Mettaton sounds very similar to Metatron/Mattatron, which is a Jewish angel. See the Wikipedia article on Metatron for more info.
Honestly? Cool idea! I don't see any relation between the two, though. Metatron is the “celestial scribe”, while Mettaton is a showman.
(P.S. Congrats on your first post!)
OR what if it's secretly a message spelled backwards?!
nottateM
nott a teM
Well it's true at least.
Facinating
Spamton backwards is:
notmapS
not mapS
also true
tenna backwards is An Net
Tenna is secretly a fishing net in the light world confirmed
Tenna's internet
And we thought that he was a TV this WHOLE TIME!
AHA!
I CAUGHT you!
Online!
Outside FractureTale!
WHen you said you couldn't finangle yourself any more time!
NYEHEHEHEHEH!
Bro this is just
Kris 
backwards THE ROARING KNIGHT 
what how
The mystic text The Book of Enoch tells a story of Enoch, a human, becoming an angel, Metatron, which kind of parallels how Mettaton was once a ghost, and is now an invincible robot (not able to be attacked in battle).
No it's Mr. Ant Tenna
an neT tn A .rM
Kris backwards is risK, one letter away from frisK.
No it's sirK
WHO IS SIR K
Oh
(Kris, who opens dark fountains and has a deal with the Knight, is quite risky. )
Typo, it would be Kris's evil cousin Ksir.