I doubt you'll reach the point of dealing 2000 true damage within a reasonable game though. There will certainly be outlier cases where this might be an issue, but they will probably be infrequent.
(Please note I'm rounding some numbers slightly for simplicity's sake, the variation is minimal) In order to deal 2000 damage, you need 650 (+10% bonus HP) = 2000, meaning 10% HP = 1350, or 100% Bonus HP = 13,500. In order to get that with stoneplate, you need at least 13,500 + ~1900 = 15,400, and 15,400 / 2 = 7,700 HP. Also consider that this requires being surrounded by all 5 enemy champions, which rarely happens around a cho anyway, and is even less likely after this item comes out. In order to have enough with only the 3 champ trigger, you need at least ~11,000 HP (11,000 x 1.4 = 15400).
Using the smaller number (7,700 HP) for the benefit of this example, that might not seem too absurd right now, but keep in mind that health items are being nerfed almost universally (by between 75 and 150 depending on the item), Stoneplate itself gives no health (meaning between it and boots you are limited to 4 health items max), and unless you build FH (which should be part of your core on tank Cho), you're not going to stack very quickly, in which case you're taking a 3rd non HP item out of 6 slots. With that in mind, even taking two high health items (say SV and Titanic, which is pretty strong on HP Cho) and a warmog's for your other 3, you only have ~3700 health. That means you need at least 4000 HP from stacks to get that kind of damage. For reference, that's 25 stacks. Even at max CDR and using feast on CD, that takes at least 18 minutes. This is not accounting for the fact that you won't have 45% CDR right away, because of which it will most likely take you closer to 25-30. Also, you can't get more than 6 stacks from non-champs, meaning you'll need 19 ult kills on champs, drakes, and Baron/Rift Herald.
The ONLY situation I can see this item potentially being an issue on Cho is if he flashes into Baron/Drake for a steal vs a 5 man team, in which case he could get away with a 2k ult within a reasonable health range, or in a game where it has stalled past 60 minutes and Cho has been able to stack an absurd amount (at which point you're screwed anyway, with or without stonplate).