If someone, somehow, made a new, official TB-ISO Fallout title, they would probably use full 3D characters even if its 2D iso - already been done in Fallout Tactics.
A new iso-tb Fallout would probably be something like Pillars of Eternity or Shadowrun Returns - built in a 3D engine with a fixed isometric perspective, creating a illusion of 2D.
Would't surprise me if until 2025 we got a iso-TB Fallout spin-off. There's clearly a HUGE untapped demand there, all those Fallout-likes (AoD, Wasteland 2, Underrail, etc etc) didn't come out of somebody's ass. They can market it on "nostalgia" and shit.
My bet: A new Fallout Tactics game made for pc/portables. Think Fallout Tactics with the mechanics of nuXcom.