My take for first full year.
1-1.5 million= ok but on the bad side
1.5-2 million= ok but on the good side
2-2.5 million= good
2.5-3 million = great
3-3.5 million = fantastic
Anything more is unrealistic for a 500$ box. It's also near impossible to guess lifetime sales, as we don't yet know if it will play next gen games.
Halo MCC will sell 5+ million copies(including digital)
halo 5 will sell 10 million copies(including digital)
x1 will pass ps4 in USA, and UK.