Two things:
First, I like the idea someone proposed of having this be a "year-long" drop. So, if I had 10k SPS on day 1 I could get 10 cards. If, 30 days later I was able to add another 10k to my stake I could get another 10 cards. Maybe do a once-a-month snapshot for 12 months so that people who can't afford to go buy 400k SPS would have a chance to at least build their stake over time to access more cards. Would this be possible?
Second, would it just be staked SPS that is counted? Or would it also include SPS in the LPs since they are also providing value to the economy as a whole? Actually, to answer my own question, those probably couldn't count because it would be too easy to game the system by going in for the snapshot and coming out the next day.