What, another melee master trait? When I barely get a use out of MVm and have yet to get a win out of MBm (though mostly for lack of doing a quick HNTR run)? I was kinda hoping that if we'd get another master trait, it would be something you'd use in a non-AoB run.
Admittedly, the problem with melee is that there isn't much to do with it in terms of pre-game strategy: you pick your master trait and stick to it. That said, MBm and MVm basically cover what you can do with what you have. Knives are a 2d5 attack with +1 accuracy, and I'm pretty sure +melee-to-hit doesn't account for the alt fire, so by throwing it's not all that awesome of an attack, even if fired off twice in a row. If you pull it off in melee combat, after the first hit a lot a enemies will punch, and then you insta-kill them; for the melee-retarded (Revs, Mancubi, Viles), they'll probably use the chance to run away, so you instantly run next to them, hit again, and repeat as necessary. For one-on-one, you couldn't really ask for more.
This really, REALLY breaks down against groups, however. Unless they are packed tightly together (like groups of foos) you're likely to end up with a somewhat loose but grouped scattering of enemies, and absolutely no way to approach them. The current master traits account for both of these (MBm has dodging and insta-move after the kill, MVm has constant healing, both have zerking) so eventually they have survivability in these frequent situations. Not so in this build, which can rock in the early-game but has very little of a chance later (save the Cyberdemon, who's pretty much a pushover) due to the total lack of defense in nasty corridors and whatnot, as well as the limited range of the knives themselves.
For starters, if you want an instant succession of multiple knives, you'll need a way to keep placing knives into your hands. The fact that "your next action will take no time" doesn't account for the weapon's firing speed itself, a full 1.0sec, and making the attack instant doesn't account for the time it takes to reequip the knife (after the second, at least). Since Juggler is incorporated, we could try something like this: every successful hit with a thrown knife automatically places a knife from your inventory into your prepared slot. Since you likely need some EE to make throwing multiple knives at once possible (and multiple knives in the first place) this is probably a fair balance.
I dunno, in general it's a weird trait. As much as I'd like to see a good use for throwing knives (barrels and HA aside), this is a bit extreme. I'd give it a shot, but without Berserker or defense it's an uphill ride the whole way.