All they need to do is upgrade the blade part. The hilt should remain unchanged, apart from possibly the gem. OOOOO!
Maybe you should be able to imbue your blade with certain powers!
Fire- Blade burns and gem is red, sears foes, v. effective against woodland beasts, useless against water beasts.
Water - blade takes on a more bluey sheen, blue gem, good against fire, bad against wood, can be used underwater
Wood - Blade turns into wood, green gem, good against water, useless against fire, can be used like deku sticks (blade grows back)
Shadow - Blade turns black, purple gem, bad against fire, certain enemies only hurt by this
Spirit - Blade turns Yellow, Orange gem, kills ghosts with one hit, super effective against all weak normal enemies
Light - Blade burns with white fire and grows longer. Gem is White. Kills all with one hit.
At least then the people giving you their help in OoT would make sense.
Edit: Made some rubbish JPEGs of what the swords might look like. Check em out

. They are arranged in suggested abtainment order.
Normal SwordForest SwordFire SwordWater SwordShadow SwordSpirit SwordEvil's Bane: The Blessed Master Sword