^ i have often pondered on this, but would approach it in a completely different way.
1) AOTC would be episode I, ROTS would be episode II.
These would be heavily editted to the point that the entire drive of the plot would be unrecognisable. fan filmed subplots* would begin to build the pilot/wookie/soldier/smuggler plotlines that the PT missed.
the new EPIII would then be a complete fan-film about the Empire dealing with these subplots. Then when we see luke and obi-wan in EPIV, they, like yoda, would have been missing long enough to emphasise their time away from the limelight.
The advantages of cutting TPM, is that the characters and story would be much more akin to ANH, where the entire universe suggests that great events have transpired previously.
The great thing about a new 'filler' film between II and IV is that the Jedi can literally be extinct, so when Han appears to be oblivious to the jedi later on, we can understand this a bit more.
If Lucas ever does make the Live action tv-series then maybe that could be used. Until then maybe we should just dub firefly and pretend.....
*SUBPLOT IDEAS
Beru and Owen, as the han and chewie of the series earlier on, now, fleeing various entaglements with baby luke
If Padme doesn't die, stuff she could be getting on with
Replacing Dooku as we know him with Jedi Dooku, and NOT killing hm off in ROTS. The new film would maybe focus on his redemption. He dies at the end.
The emerging rebel alliance, with teenage leia stepping up later on to take more control.
Maybe something with Biggs, or the droids.
^These can all be mulched together to an extent.