I've been thinking...In The Birth of Evil Part 2 during the Emperor's battle with Aku, he tells Aku that his sword was "forged from the strength and power of the human spirit".
Now the Scotsman is a spirit after his death thank to the Celtic Magic of his sword, do you think that he not only can possibly harm Aku now but could also cleanse Aku's evil from Ashi without killing her?
I think it's a possibility...and now I've got an image stuck in my head of Aku trying to escape when the tide turns against him - only for the Scotsman to grab hold of him and say "Ha Ha Ha! You're not going anywhere, you big baby!"