How many do you think are eligible for the club today? I would think it is far less than 5000 individuals, maybe closer to 500.. 
surely can't be more than 10000.
Another guesstimation I just did puts the upper bound at ~611 members conservatively: satoshi: 1 million, 2 guys 500k, 4 guys: 250k, 8 guys: 125k and so on.
I'm guessing it's around 300 people in that club max. Tendency: decreasing.