Since GT++ already adds in gelid cryothermium (and puts it to use with cinnabar) without Thermal Expansion, which is very useful for packs like Beyond Reality that use Ender IO instead but do have Big Reactors, it might be worth considering having GT++ add back other materials and fluids useful for Big Reactors like resonant ender and enderium.

Enderium was never initially added because Gregtech already added it.
This will require a simple api branch check with a try/catch to try add it, since it's rather impossible to differentiate between .09.01 and .09.27, for example.

Not really sure why I missed resonant ender though.

a908643 re-adds Resonant Ender.

Enderium I will do differently, but expect it in the next day or two.

daa2a60 re-adds Enderium by default into GT.