I truly appreciate, and even encourage, consideration of YAGNI when writing software. However, I think it must be made clear that YAGNI was conceived in the context of an end-user application.
If you're going to write/maintain a standard library, YAGNI no longer applies. Case in point, in Python 2, there is exactly *ZERO* ways of converting a datetime object into a timestamp; however, there exist several ways of converting a timestamp into a datetime object.