What about optional date_epoch on items ?

[steamboatid]

IMHO,
date_epoch is the most portable date format acros platform, OS. etc.
It's easier to convert to other human readible format.
Maybe at version 1.2

[manton]

I think the current format is more standard and easy enough to parse, and it's also human-readable if someone is looking at the feed directly. Thanks for the suggestion, though!

[steamboatid]

one of important factor compared to rss or atom is that json is easier for machine to read.
so, IMO,
human readable format less important machine readable format