1. How does it compare to the EX1? Does it replace the EX1?
It probably doesn't replace the EX1, since the EX1 has 1/2 inch imagers instead of 1/3 inch. Also, they just updated the EX1 with the EX1R, so clearly it's not going away for a year or two. The EX1R sells for $6,299.
2. Does this replace the Z5U?
Probably. It's essentially the same body, and HDV is dying. Given the pricing/features of the EX1, this gives us a good idea what the NXCAM will sell for (the Z5U sells for $4,095.)
2. AVCHD? Why not XDCAM EX?
Since Sony owns XDCAM, it's probably not a licensing issue. AVCHD takes up less space (24 vs. XDCAM EX's 35 Mbps) and given recording to flash memory, size is probably a big consideration. Both are 8-bit, and 4:2:0.
AVCHD gets a bum wrap because it's mostly been in consumer cameras, often at the lower bit rates (24 appears to be the maximum for the standard at the moment.) But it's also a more efficient compressor than MPEG2 (which can be a negative when editing.)
3. Low bit-rate? Only 24 Mbps?
XDCAM does have a higher bit rate, but the H.264 compressor in AVCHD is more efficient than the MPEG2 compressor. Some people think AVCHD rivals XDCAM EX (not to be confused with XDCAM HD.)
4. What? $4,000? Anything cheaper?
Since this seems to replace the Z5U, if Sony follows it's current practice with the FX1000 semi-pro and the Z5U pro cameras, there will probably be a semi-pro model soon after that lacks the XLR audio input, selling at around $3,000.