Since the current behavior is explicitly documented in the code, I suppose that settles it.  I really can't imagine a good use case for it, though.  But then again, until I filed this ticket, I didn't know that append-next-kill could sometimes prepend instead of append.  It seems a small miracle that I've never stumbled across the prepending function by accident.

Perhaps kill-whole-line does technically kill both forwards and backwards, but to me it's always been just a welcome shortcut for the classic Emacs idiom C-a C-k C-k.  And the name kill-whole-line certainly implies to me that the line is killed as a single unit, not killed in two steps in opposite directions.  If the current behavior is to stay, then I think it could stand to be called out explicitly in the documentation for kill-whole-line.

Anyway!  Although I'd prefer to see what I'd consider to be the more sensible behavior built into Emacs, I can achieve it on my own by just rebinding C-S-backspace to a command that moves to the beginning of the line before calling kill-whole-line.