Okay, bear with me here. A lightsaber is just an arc of plasma inside a magnetic containment field, right? We already have similar technologies, the only real implausibilities involve things like a compact enough power source and tackling overheating issues.
But imagine if the D’ni could use the art to make lightsabers, specifically using the principles of Takes made by the Bah’ro in the fifth game. These anomalies are capable of existing in two or more ages at once, and allow direct physical contact or transfer of things through multiple ages without requiring a dynamic link along the lines of a book or tablet.
First let’s assume that, unlike Aperture portals, Bah’ro Takes can be freely moved in three dimensional space without compromising their structural integrity or functional use. If this is the case, it should be possible to build a tiny take with an elongated linking bubble, and attach it to a handle. Within the hilt could be a power source, if such a thing is required, and a way to activate and deactivate the link.
Next, write (program, align, however these work in particular) a way for the Take to link to an age that has already collapsed to the point that it is entirely supernova, or just write a link to the core of a sun. According to conventional rules of the Art, a living being is required to trigger a link, at least in the case of books. If the bubble of a Take works the same way, it should be sufficient in containing the plasma of a star. Upon contact with a living being, they would pass through the bubble and be burned by the energy within the Take.
For fun you could say that some Rime crystals could go inside the hilt that change the age the Take links to, which changes what type of star is present, giving the same effect as having differently colored lightsaber crystals and blades.
The big problem I see with this is that, because non-biological entities will not trigger the link and penetrate the bubble, they could not be used to cut through solid objects. It may be reasonable to assume, however, that two Take bubbles coming into contact with one another would deflect, as intersecting them would cause recursive linking.
