The article states that the JPL plan only considers the energy generation to be a useful byproduct.
If the risk were truly imminent and quantifiable, I assume it would be pursued however absurdly exotic and fanciful it seemed on its face.
On the other hand, defusing a volcano on a timeline of a thousand years or longer would be politically challenging. That might see the dissolution and construction of multiple states (here, electric power generation may help assure survival). Add in that civilization can't seem to get its head on straight about comparatively faster-acting climate change, for example, and can barely prepare for an earthquake.
At least imagining an exploding apocalyptic supervolcano may elicit more visceral emotions.
Still, it doesn't appear there's much cause for worry so it's only a brainstorm.