With the way the BT is setup, its rarely occurs, unless you are a small server doing 1vs1 or something, and then its hardly any advantage, since you only have one target anyways.

If it happened more in team modes with 12+ players it would be funner.

My idea was that BT would trigger once you acheived a triple kill or multi kill(unless you had specials on, like pred, flame, etc, no bt then).
Or perhaps have an item that caused BT to trigger, similar to pred or berserk.
And for the player that triggered the BT, they would get slightly faster reload time than everyone else, or some other advantage.
Maybe even extra kills would make BT go longer (that may be too much though)

Now when the BT triggered, it would be a limited time, like seconds, and happen on the entire server.

I just thought BT was a great update, but its hardly ever noticed. I'd love to see it play a bigger role in the gameplay.

Now is this even possible?

*Also, would a bullet dodge move be plausible? Like SSB-Melee's air didge? A one bullet dodge, based on a charge metter liek jets. K that's all.

No, I think the BT is fine as it is now. No need to modify it.
If you don't see it often this is because you don't play often, or only on over crowded servers (which is stupid in my opinion).
NO.

It's fine the way it is. If you make it trigger when players are far away from each other people will get frustrated for the screen slowing down when they're just running around and not doing anything.

That's true, the ones of will get a little screwed over, not knowing what's going on.

And I liked crowded servers, which where most powerful ownage skills can come from, imo.

But now I'm more interested in these miniture maps that feature constant BT.

Just play Arena2 or '3, or DeMonIc's Niebelung. Those are so small at least half of all the kills on-screen will trigger BT.