Excellent! I’ve also long pondered a Machete Order fanedit inspired by Topher Grace’s cut and came to a similar conclusion: use just the Darth Maul fight, ending with Obi-Wan’s promise, as a cold open in between A Long Time Ago and the Main Title.
I love your voiceover intro; very smoothly sets up the shift in time period without resorting to an out-of-place ’35 Years Earlier’ subtitle, wasting words in the opening crawl or even spoiling the surprise cold open.
As I’ve never tried editing this, I don’t know if the Darth Maul fight's energy could be sustained without cutting to the space and Gungan battles. Your flashbacks sidestep this issue nicely.
I’m glad you're putting it into action – ideas are worthless without execution!
I do have one suggestion. The cut after A Long Time Ago needs to be as explosive a start as the usual Main Title and possibly Duel of the Fates can’t pull it off by itself. It may work better to cut straight to the flash of a lightsaber strike – possibly from the flurry of blows just before where you started the scene – and amplify that striking noise.
Looking forward to seeing the finished product!