IF it's really going to be as you describe, then I love the name "Juggernaut".
EDIT: Please note that "Oh yeah, the names need to be empire specific too since we've added empire specific weaponry to each empire's Sunderer" was edited into the above message above AFTER I only came up with a single name suggestion, otherwise I would have suggested 3.
Homey
''Ravager'' - VS
''Pillager'' - TR
''Conqueror'' - NC
Some other options (no empire suggestions attached):
''Subjugator''
''Vanquisher''
''Devastator''
qm
I second the notion of Juggernaut for the NC variant.
TR= Rhino
VS= Nova
NC: Vindicator VS: Leviathan TR: Retributor Common pool: Juggernaut
Or some variation of those if one of them goes better with a different empire.
I tried to make them fit the empire themes. "Vindicator" for the NC, since they want to vindicate themselves as superior to the TR oppressive rule. "Leviathan" for the VS since they're sort of sci-fi ethereal, and the Leviathan is a giant monster from ancient mythology. "Retributor" for the TR since they want retribution against the VS and NC for rebelling against the Republic. "Juggernaut" for common pool since this thing sounds like a big, bad-arse menace, and it's a neutral word that doesn't sound like it should be especially associated with any of the three empires' motifs.
i was thinking:
tr: executor (egg-zec-you-tor not ex-ecutor)
vs: victory
nc: condor (birdy?)
or
tr: executor
vs: Annihilator
nc: victory
obviously you can change around the names for each empire but i was just specifying all the names i think would be good, aspecially the tr's executor