A Han Solo might work but they would have to really, totally nail it with the casting.
I've never been a huge Boba Fett fanboy. A solo movie might demystify him too much. But I'll still go see it.
My only question at the time was who was the actual Phantom? The secret Darth Sideous guy (who was obviously McDiarmid), or the secret Darth Maul guy who had five lines? Lucas did a shitty job of making that clear. (And now I remember the Yoda line at the end of the movie, so yeah. But still.)
From dictionary.com, "phantom":
2. an appearance or illusion without material substance, as a dream image
, mirage, or optical illusion.
3. a person or thing of merely illusory power, status, efficacy, etc.: the phantom of fear.
I think perhaps the "Phantom Menace" was the Trade Federation and their invasion of Naboo. Senator Palpatine manufactured this threat to Naboo so that he could get himself elected Chancellor in place of Valorum.