I say radical because they go against the grain as far as the mod is concerned.
A new suit, called a lava suit that can sustain the player in lava if there are enough coolant cells. Perhaps some way the player can see through the lava for ore harvesting or something.
Multi-block solar like those moving solar panel things with light sensors that add efficiency and could be used to combine multiple solar panels into 40% more efficient ones. Which might mean the regular solar panel would need to be nerfed.
A mult-iblock nuclear reactor, slightly more stable than the current one. First you have the reactor chamber, two pumps that push coolant through pipes to the reactor rods. A heat exchange chamber which could be about 2x2blocks then an output pipe for the newly heated water to a generator which would output the steam to a cooling system in the form of heat exchange pipes surrounded by water. For reactor melt downs it could leak radiation and if bad enough explode.
And perhaps a new super suit, unlike the quantum suit it should be able to fly and have its own reactor. Perhaps some waste from a nuclear reactor run through a multi-block particle collider to make the specific element needed for the reactor that would need to be periodically replaced.
Maybe another reactor a step up from the other reactor, though completely dependent on it for making heavy water and tritium.
Perhaps some tier four or five machines to match and take up the produced power.
Like a portal that takes the user to another land, like the moon or mars.