Hey I saw your post on the brawl peach boards (since I decided to namesearch.) I'm glad you at least decided to ask about it... was kinda worried it'd be completely ignored.
The one important detail I didn't mention in my post was that it is more difficult on shorter characters. You must be in the air to drop the turnip, and it takes a bit of time to hit them. Peach rises as the turnips falling so the footstool becomes difficult on shorter chars (unfortunately and notably, MK.) I’m not sure what works with the buffer system, but if you could buffer the zdrop for the first frame of your jump it would be very beneficial. That said I’ve been able to at least do the zdrop to footstool on every character I’ve tried. (Which is why this is significant for peach, it works on everyone.)
The other problem with the different heights is it changes timing for the drop -> footstool. Similar to Icy stuff (I assume in brawl, but definitely in melee,) for them the weights of characters change the timing of their CGs, which can cause Icy players to mess up.
It’s also technically not an infinite because eventually the turnip will disappear, but peach will be able to pile on enough damage to kill anyone with an usmash well before that happens. I also am not sure how to recatch the turnip every time (it would work for me sometimes but often wouldn’t.) I thought I read skimming through the thread that Peach will catch it when she drops out of float?
Certainly makes a lot of buttons to press in a very short time period. Jump->instant zdrop->footstool->instant float->aerial->drop float (to catch turnip)->space aerial properly to continue the lock. The best news about that is it’s 1 button at a time; just in rapid succession. YZYdownAneutral. Of course if you’re locking beforehand you’re probably clawing (at least that’s my preference,) which makes Z tougher to get to. Probably setting X or another button to Z would be good. Doing bair with cstick would also probably be better than A. I don’t need to tell you this stuff; you can figure it out on your own.
But yes, peach’s infinite is very (extremely?) difficult and tough to set up, but I remember there were things at the beginning of melee which were too difficult to ever be viable but are now standard in tourney play. Plus if you get it even once in a match, that’s potentially an entire stock, which is a pretty/really big deal.
I think that's all the followup thoughts I have on it. Not easy, but once applied consistently should jump Peach a tier or two. IMO she has HUGE potential in brawl.