The version of the Prometheus in Voyager, where it first showed up, was a prototype. The muti vector feature was deemed too dangerous and impractical. That feature in the Prometheus was designed out of the final production space-frame as a result. Saucer separation is used for emergencies only.
As far a s Cryptic is concerned; its not going to happen. There is no feasible way to implement MVS in a manageable or meaningful way.
I think Cryptic should seriously consider it. Have it as some far flung skills or tactical console.
The technical basis for implementing Ttri Vector Assault Mode exists in "photonic fleet". It'll be a no brainer to extend that to Prometheus class ships. What it does, or what it buffs, is for Cryptic to determine.
p.s. the way the game is currently designed, TVAM is definitely a bad way to attack your enemy as it spreads your fire really thin, across many shields. But the coolness factor is through the roof! And it's easily doable
Multi-Vecto assault on the Prometheus was all automated. No one was piloting any part of the ship, it would just do it's thing and then recombine.
Computer: "Multi-vector assault mode activated, please designate attack pattern."
Doctor: "uhhh..... Alpha"
Computer: "Confirmed, please designate target."
Both Doctors: "Romulans!"
*ship goes and blows up a Romulan vessel*
I imagine in practice it would be fairly impotent to be honest. Sure it'll work most of the time, but what do you do if the center section gets blown up while the ship's separated? What if the docking mechanism is damaged by enemy fire while the ship is separated and it just grinds itself against the other portions when they try to recombine? What happens if the docking mechanism is damaged while the ship's still combined and it can't separate.
The Galaxys were designed to separate to keep the Saucer section OUT of combat (hence "battle bridge). Occasionally the saucer would see combat by necessity, but overall not the intention because, like the Tier 5 Escort Database says about the Prometheus, the separation system is too prone to failure.
But ignoring all that, assuming they did give it to us in game, you wouldn't suddenly turn into 3 ships and attack, It'd probably be an ability or 3, hit the "Multi-vector pattern Alpha" button, your ship leaves your control for a few moments, splits, attacks the enemy from 3 different angles, recombines. you're back in charge.