Help with great weapon fighting. Designer required

Ello friendos, i'm in a west March server and a rules question came up regarding the great weapon fighting 

"When you roll damage for an attack you make with a Melee weapon that you are holding with two hands, you can treat any 1 or 2 on a damage die as a 3. The weapon must have the Two-Handed or Versatile property to gain this benefit."

Was it intended for it to work on the extra dmg of flame tongues, vicious weapons or even dragon wrath weapons? Or was it only intended for the weapon's base dmg die? One of the new designers from DND's team insight would be helpful. 

The designers of D&D don't really frequent these forums.

This Sage Advice answer clarifies that Great Weapon Fighting is meant to work with the weapon's damage roll, but not with any separate add-on damage effects. So, the question is whether the extra damage from weapons like Flame Tongue and Vicious Weapon is part of the weapon's damage roll. It certainly seems to me like it is, since these weapons say that the extra damage is "from the attack" and not from an external source, and that's the way I've always ruled it.

I don't think there's been any official ruling on it.

It is worth pointing out that Great Weapon Fighting is a pretty weak feat already, and if you don't allow it to be used on things like this, it's probably not worth bothering with at all.