Agony Resistance Mechanic
You’re asking us questions we cannot answer, because we have no ascended armour/weapons and we can’t tell you in the future if agony is Fractal-exclusive or not.
My guess is that it will remain a FotM mechanic, for the simple reason that those of us who have 45 AR will already have a huge pre-existing advantage compared to people who don’t do FotM. When they introduced temporary content, you can easily access those places (to take the most recent examples, either from Lion’s Arch for Southsun or low level areas for Flame and Frost like Diessa and Wayfarer) and in Southsun and that Molten dungeon you’re scaled to 80. It seems silly to release some new dungeon in the future that requires Agony Resistance because some players, especially new non-80s, won’t be able to access it off the bat.