Now the weapon itself… felt sort of underwhelming, considering the effort put into getting access to it. It’s essentially not that different from a vibro-katana or bastardsword save for the +1d4 Energy Damage Bonus. Which doesn’t getting displayed seperately in the combat log, so it’s hard to say whether it works or not.
My suggestion would be to increase the base damage to either 2d6 like pistols or even 2d8 like rifles. That shouldn’t put the lightsaber too much ahead of other weapons. Another thing are the mod slots, I’d switch the red and blue slots (so it would 3 blue and 2 red at MK IV). That way a lightsaber would be more use to a Force user.
I’d also add the Extra Melee Damage Type (Energy) to it (and the ranged equivalent to all blasters) and if you want to the extra length … put an appropriate Light [dim] or [low] (color) on it.
The Extra Melee Damage Type property basically just changes it from Slashing to Slashing/Energy
Edit: Another solution might be to add a new Force perk that improves lightsaber damage (with the restriction of “must be wearing Force armor and wielding a lightsaber or saberstaff”) . That way the lightsaber would still be an option for non-Force users, while it would be deadlier in the hands of a trained Force user.