Based on the concrete yardstick of "lakh lakh lok" - I can vouch for a 35-40K sitting capacity for BNS.
By the way, you gotta wonder what lakh lakh lok do at this meetings where nothing really happens. The words that come out of the Bokta's (speakers) don't even count as BS and there's really not much entertainment as most BOKTA's have no clue what they are blabbering about. Then again, this issue is better served for a different kind of board.