I vote yes.
Why? Because Phobos has needed a solid module for working with dates and time for a long time, and neither std.date or std.gregorian filled that need -- std.date is buggy beyond repair, and std.gregorian's API doesn't make my normal tasks easy. std.datetime's API is fairly intuitive, and what I would expect out of a fairly modern date/time library. There are some bugs over here the need attending to, but I believe that the API itself is solid, and well designed, and that it can be a solid, good quality module in Phobos.
