Because it will be a completely different game I guess. The DS version is surely going to be way different since it's a Q port. It might be way better or it might be way crappier (hello Every Extend Extra Extreme). At any rate it will surely include the Rez/Lumines/E4/Meteos/Gunpey syncing the music with the visuals thing because that NEVAR GETS OLD!
Yeah I think it'd have to be segmented to be remotely worth watching. You can segment after every shot by backing up your save file to get, as you say, perfect shots with every ball. They'd be unlikely to be especially BIG shots though, at least not after the first two or three, because it's faster to clear, say, two oranges with two shots, each bouncing off an orange and going straight down into the bucket, than to clear two oranges with one shot bounced between them. Also, you'd want your final shot on each level to bounce straight off an orange into the 5000, and for it to be your final ball, to minimise the time taken counting up points. Also, some of the special powers would be positively BAD and you'd want to avoid them - particularly Spooky Ball and Zen Ball. Finally, I think it's possible to hack the game / your save to give yourself Super Guide or Zen Ball - this could be potentially useful to help determine what your best shot is, and then you'd just return to the legit save and record yourself executing the shot. Finally, the main timesaver of this run will be, of course, luck-manipulating each level to give you all your oranges in a big cluster you can clear in one go. I expect you'll need to load each level dozens of times to get a useable one. Given the number of levels Peggle has, the amount of work that you'd need to put in to get a respectable run would be a lot - but by all means do it if you want to. I'd love to watch a run of Peggle if it was actually good.
Edit: Make sure you quit to the main menu well BEFORE each shot ends. Then when you reload the game, you'll have the time taken before the ball gets to the bottom to line up your next shot, meaning that you'll spend zero time in the whole run actually aiming shots (besides occassional waiting for the bucket or moving blocks, I guess).
Edit 2: By the way, are you planning on doing campaign mode, or individual levels? Campaign mode would be cooler to watch IMO, but doing individual levels would allow more competition.