Oh, that's right. Just using VP's as the tiebreaker... there's a difference here from Nova in that Nova's 8 rounds are guaranteed to produce a single 8-0 person as long as there aren't more than 256 participants. So tiebreakers can never be what actually crowns the champion (or 2nd place for that matter, since there would only be two undefeated ppl at the end of round 7) at the Nova itself. That's a little different from saying "we know that there will be multiple ppl with perfect records and we'll use Tiebreakers to figure out which one of them won the event".
But, I actually kind of like that idea... you'd have to keep in mind that, although it doesn't actually help you get a W in any particular round, accumulating victory points is always something you want to be doing & is the only way to actually win if you DO end up 3-0.
So, when considering a format, I suppose it's inevitable to ask "what kinds of armies does this favor"? If we use pure VP's as the means to rank the 3-0 players, this certainly favors "glass cannon" type armies who are good at killling but not so good at surviving, because you don't get any VP's for having stuff left on the table.
For an extreme example,
if you have army A that has the following scores:
round 1: I killed 1900 pts of his army, but I only had 150 pts left on the table
round 2: same
round 3: same
and army B that has the following scores:
round 1: I killed 1800 pts of his, and he didn't kill a single model of mine
round 2: same
round 3: same
Army A would win.
What if we use VP DIFFERENTIAL as the tiebreaker, rather than raw VP? Then it would favor neither offensive (like Imperial Guard) nor defensive (like, say, Nurgle Daemons) armies.