Anything ultra rare could fit the bill, however an assumption is that the thread is asking to select a card that is somewhat available and auctioned more than once in a blue moon.
Picking anything Ruth, Cobb, Matty, WoJo, Wags or Young would be tough but not ruled out unless it's the T206 Wags because it's already pretty pricey and a huge % increase may not be too likely for that card. Also, sticking with a "card" would eliminate a W600 or other cabinet.
The way things have been trending it will probably be a "high grade" card that could be somewhat widely available but not in a high grade.
T202 Tinker - Evers - Chance in a "9" or "10" grade? It's kind of a cool card because it's actually Tinker >> Evers (center panel) >> Chance from left to right.
No idea.
I'd be the last to guess correctly because I've sold so much good stuff before it took off.