Does NXT support multiple senders / receivers in a transaction (CoinJoin)?
BTC is doing over 100,000 transactions per day now.
IF NXT became that popular, then that would be 100000/1440 ~= 69.5 transactions per block.
So, that leaves plenty of room for growth. As is, NXT can support up to 367,200 transactions per day.
Looks like you've thought it through pretty well, but what happens if you need more transactions per block?