The Division 2 has a long way to find balance in its PvP, but for now, and if you like sub machine guns, this build is probably you for you. A few people in my clan, and YouTuber, Widdz, have been using this (or variants on it). While it's too early to say whether it's meta defining, there's no doubting that:

1. It's a lot of fun.

2. It offers ridiculous sustain.

3. Has massive damage potential. 

4. Still works well in PvE. 

5. Only really weak consistent long ranged attacks.

Overview

This build utilises the following:

• High critical hit chance (cap).
• High health pool.
• Rapid fire weaponry (SMG).
• Use of the following weapon/armor Talent(s):
  • "Clutch" to restore 15% of your health and repair 2% of your armor every time you critically hit. 
  • "Incessant Chatter" to gain 1% rate of fire (max 60%) for every shot you land. 
  • "Box Magazine" to refill 20% of your magazine when you gain a kill, while also increasing magazine capacity.
  • "Blabbermouth" to 20% increased rate of fire when your weapon is holstered, and you reload after a kill.
  • "Allegro" to increase rate of fire by 10%. 
  • "Strained" to gain a total of 200% crit damage when your armor is depleted (10% gained per 5% lost).
  • "Berserk" to gain 10% weapon damage for every 10% of your maximum armor depleted.
  • "Vital" to increase Health by 20%.
  • "Patience" to gain armor restoration when hiding in cover for more than 3 seconds.
  • "Safeguard" to gain 150% bonus to repairing and healing effects for 20 seconds after killing a target.
• Any weapon modifications which improve your critical hit chance or increased magazine size. 

Loadout

• Primary Weapon: Vector SBR 9mm
  • "Strained"
  • "Allegro"
  • Third Talent is your choice. 
  • EXPS3 Holo Sight (12% crit chance / -10% headshot damage)
  • Laser Pointer (10% crit chance / -10% stability)
  • Loud Vent Brake 9mm (20% optimal range / -10% stability)
  • Extended 9mm Mag (+10 Rounds / -5% crit chance)
• Secondary Weapon: The Chatterbox (Exotic) and/or P90. 
  • "Incessant Chatter" 
  • "Box Magazine" 
  • "Blabbermouth" 
• Demolitionist:
  • "Crisis Response" allows you to fully reload when armor is depleted. 
  • "X-Stat Armor Kit Supplimentary" boosts weapon handling by 100% when using an armor kit repair (also pairs with Safeguard). 
  • "Spray and Pray Tier 3" boosts SMG damage by 15%
  • "Braced for Impact" mitigates one explosion every 60 seconds.
• Chem Launcher (healing): Provides clutch healing in a real pinch.
• Crusader Ballistic Shield: Similarly to Chem Launcher, provides pinch mitigation when needed.

Other than the above, when it comes to armor and modifications, just ensure you first get your weapon loadouts based on the above, and then move to align these remaining components to provide bonus health, weapon damage, and crit chance (unless capped), at which point ensure your backpack has "Safeguard".

Video