Decimal time support in 'date'

[za3k]

I am interested in adding support for decimal time to 'date', but before 
I dive into writing a patch, I wanted to ask whether the patch has a 
chance of being accepted--this may just be too obscure.

In decimal time, 2019-12-12.75 would represent 2019-12-12T18:00:00. 
Decimal time in the modern era is mainly used in timekeeping (to track 
employee or contracting hours) and in scientific recording (to make 
drawing graphs easy). Astronomers use another form of decimal time on 
their own calendar and would not be supported.

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Some planned specifics
The calculation is straightforward: Divide the number of seconds elapsed 
in the day by the total number of seconds in the day.

Based on my research, anyone who cares about accuracy uses standard 
time, so there is not an established standard on how to deal with DST 
changes. My plan would be to divide by the correct total number of 
seconds for leap seconds, and to throw an error if the locale has a DST 
change on the day.

The internal implementation width would be 14 digits (slightly more than 
nanosecond accuracy). I would follow the convention set in %N that the 
field truncates, rather than rounds, the decimal value. The default 
printed width would be 5 digits (slightly more than second accuracy).

I will not include parsing support, because of issues with rounding, and 
potential confusion with standard date formats.