I'm going to let Rob Beschizza from Gadget Lab speak for me here, not out of laziness (only partly), but simply because he puts it so damn well:
If Jules Verne had invented a lightsaber, I wonder what would have come out of the hilt. An ionically charged spurt of charged phosphorescent gas, discharged with the turn of a valve and combusted by a flint?
In fact, the entire Star Wars cycle envisioned as a steampunk saga is a wonderfully satisfying thought: Han Solo, for example, as the Colt-wielding pilot of the Millennium Zeppelin. And the very thought of Steampunk Vader makes me get weak in the knees.
Steampunk Lightsaber [Gadget Lab]
