The solar easement is one of the most ancient and venerable servitudes on land there is. Presumably it would still exist in the 24thC.
Depending on the situation, you could get a court to outright enjoin your neighbor from building a structure that would block a significant portion of the sun's light. If the building merely destroys a "scenic" view, and if I remember correctly (property law = not my favorite), you would at least be able to sue for damages to the value of your own property, if not an injunction.
Now, of course, as I've said before, "damages" are meaningless in an economy without money. So I guess it's either an injunction or nothing.
