But what is the significance of the term "seats"?
Keeping it simple… There are 30,000 seats. So let’s say NastyMining mines a block tomorrow. The 3.125 BTC would get split up and paid out to the seats (with 25% going to NastyMining) so each seat would receive approximately 0.00007812 BTC. Using similar logic, NastyMining is currently sitting on more than 16 BTC that is essentially owned by the seats.
So you could redeem your seat for BTC? Or whomever owns the seat at the time (if a block were to be mined), then they would get paid out immediately with whatever address they submitted?
each seat must hit the threshhold for pay out - iirc - it is .001 btc per seat before they will receive payout.