Mine would have been Ashi never being a thing and Jack, the Scotsman and an army of the people Jack helped, fighting Aku, kinda like what we got, but the difference being that during the showdown there would be no power of love bullshit or Ashi bullshit, Jack would instead 1v1 Aku.
During the fight Jack would trick Aku, maybe give Aku false security by pretending to lose or not have his sword, Aku being evil, would gloat and banter then Jack would bait him into opening a portal in time since the Shogun of sorrow must still be strong enough to pull it off, or maybe he'd like to show their past selves his success.
He falls for it and Jack takes his chance and goes through the portal.
Cue Aku realizing he just fucked up badly.
Back in the past, Aku just finished sending Jack into the future, he's still recovering and wondering what the hell was up with that mortal, then a new portal opens up behind him, Jack flying out of it.
Aku turns around "What!? H-HOW DID YOU RETURN!?"
Wide shot of Jack closing the gap on the weakened Aku
Close up of Jack's determined face as he swings his sword, cutting the screen as it goes
The screen transitions seamlessly to pic while the the sound effect plays, taking the entire show full circle.
Roll credits with still images of Jack returning home side by side with images of a future without Aku and finish it with a shot of Jack's family shrine, way into the future, still well kept.