well it's expected to be Q3 of this year... so that means either august or september.
IF things go smoothly with no issues.
course, 1.4.1 is the ACTUAL final content update, adding the princess, along with some additional changes to worldgen such as increased pyramid chances and discouraging the evil biomes from overlapping with the jungle and such...
so 1.4 is more like a huge stepping stone rather than the end goal.
who knows WHEN we'll get 1.4.1, we may not see that update until next year.