I would like to see some performance stats on 8x8 MIMO. I am betting that, with higher order MIMO, the throughput gains start to get more and more marginal. Those spatial channels have to remain as orthogonal as possible; otherwise, they interfere with one another.
The other consideration to remember is that 20 MHz TDD is basically the equivalent of 10 MHz FDD. So, even if Sprint has three 20 MHz TDD carriers, that 60 MHz bandwidth equates to about 30 MHz FDD. Soon enough, VZW and AT&T, maybe T-Mobile, too, will each have at least 30 MHz FDD total among their Upper/Lower 700 MHz, AWS, PCS, Cellular, possibly even WCS holdings.
Sprint cannot afford to be the slowpoke again by having similar bandwidth to that of the other operators but letting unlimited home broadband users siphon off capacity with their usage. Sprint needs to regain the perception of having faster data than at least one of the other big three mobile operators. If not, the outlook is grim.
AJ