Support for converting Epoch to readable dates

Some tagging tools like JRiver Media Center like append a "days since Epoch" tag for full dates, instead of having a formated, readable date. JRiver stores this in JR/DATE (JR_DATE in Vorbis Comments)

JRiver then replaces the actual date field with just the year and adds it's usual shenagains onto the tags.

After. Yellow is the tags that JRiver added and red is the tags that JRiver forcefully edited. The tag enclosed in a red box is the one I want to target:

Removing the other tags is easy, but no other tagger than JRiver (and Yate, although unsure because I do not have it) is able to convert Epoch to a readable and formatted date
When the date converter is used it'll format it to either Windows' date settings, YYYY-MM-DD or a user specified format.

What exactly do you want to see?
The Tag JR_DATE with something like 2015? Or 2015-05-27?

What should 42149 be? Wednesday, May 27, 2015?
The so called "Days Since 1900-01-01"?