Support for dates before 4713 BC

Hi all,

I'm working on the open source project OpenAtlas (https://openatlas.eu) which is used to enter historical and archeological data.
Although we really appreciate the wonderful PostgreSQL software, the limitation of not being able to use dates before 4713 BC is problematic in regard to archeological data.
The only reason for this limitation I found was that the Julian Calendar wasn't created with this in mind. The only suggestion I found was to write an own implementation just using integers for years. But building a parallel date system in this case would be way to cumbersome and error prone, we really like using the database for date operations.

So my questions are:
Any chance to add support for dates before 4713 BC? We really would appreciate that.

The 4713 BC limit feels very arbitrary, what is the reason for this exact limit?

Feedback and pointers are very welcome,

Alex