That's an interesting angle. If the only purpose of that is to race other combo decks, then you would want to be sure to have the 4th Natural Order in there as well. Also, you might want a MD Ruric Thar if you are really gunning for combo that hard. What would you cut for this Crop Rotation? And is Cradle really the card that wins you the matchup in these scenarios? I think going to 4 NO, 1 Ruric main is probably more effective. Also making sure you have plenty of discard in the board. When I'm racing another combo deck, I'm not sure that a Cradle is necessarily what I need the most. I would imagine that I'd want a Natural Order and 4 mana and that's it. The idea may be more clever/cute than effective. I haven't seen Sneak and Show running around in quite awhile, although I would agree that Storm is on the rise. Having a MD Crop Rotation was commonplace back in the day before 4 Cradles MD was standard. Again, I'm not sure a 5th Cradle is better than the 4th NO + Ruric. That random Crop Rotation would also suck pretty hard against the Delver decks. That's just some food for thought.
1. If you want to beat up combo, I'd keep the 6 discard and cut something else for Ruric. From your list, I'd probably cut a Pithing Needle. 6 discard is pretty standard. I don't see the logic of head hunting combo decks by cutting a combo SB card only to replace it with another combo SB card. If anything, wouldn't you wanna increase the total number of combo SB cards? Also, Cabal Therapy is your best card vs combo. Well, aside from Ruric Thar in play.
2. Progenitus is mostly helpful in matchups where we are already favored. I have cut him entirely due to the feelbads of drawing him more often than I'm able to NO him into play. If you have plenty of Pyroclasm decks running around then sure, keep him in. But from what I recall, only Miracles and weirdo RUG Delver players ever touch Pyroclasm. And Prog isn't the best guy in those matchups.
3. Depends on your meta. K.Grip is more versatile, perhaps. I think Julian likes it over the 4th Decay. Decay is better vs Delver decks.
4. Here's who plays Crop Rotation: elfbros who can't afford 4 Cradles and are using Rotations as proxy Cradles until they can get enough $$ for the real thing. There's no shame in that. And 2 Cradle/2 Rotation used to be the standard before the Legend rule allowed us to rock 4 Cradles.
You shouldn't feel like you need to change up your SB just because some schlub posts a Top 8 list with his meta-specific sideboard. Nobody can tell you how to customize your sideboard better than YOU. I get the feeling that you're trying to adhere to some kinda SB Standard List that doesn't necessarily exist. You fly free, my elven child, and determine your own destiny!

