See now there's a problem with both options.

1. Put the current 2 DR:EX dungeons into DR:High

This would cause the new DR:EX to be a coinflip again if we are to trust the info that they will be releasing 2 dungeons per patch. Inevitably will end up the same as the current situation with Neverreap and Fractal.

2. Add the 2 new dungeons to the current 2 in DR:EX

This is somewhat a bad thing because the people who are sick of Neverreap and Fractal will be even sicker of them come 3.1 especially when RNG dumps you in either of the 2 multiple times throughout a span of days.