The tricky part of removing the pay-per-block is it makes a Hot wallet/Cold storage become a necessity. Hot Wallets have their own vulnerability to thieves and cold storage adds more work and book keeping and accounting files. Just ask Eleuthria, its do'able but takes time to get it right.
At times there are 6 blocks in the wallet.
Yes 1 block, 6 blocks, 12 blocks. How ever many. That's a far cry from the complexity of 5000 Users, each using the pool as a sort of wallet/bank. The real time holding will grow with every block we solve. A dozen blocks waiting for 100 confirms before distribution will become a small slice of a pools wallet system.