In input mode, using the stty kill character should be the same as saying ^U

POSIX says: "The current kill character (see stty) shall cause an
equivalent action to the -U command, unless the previously inserted
character was a , in which case it shall be as if the literal current
kill character had been inserted instead of the ."

On Linux, the kill character seems to be ^U by default. If you change it:

stty kill ^X

In classic vi, ^U then just inserts a ^U and ^X becomes the line-kill character.
In nvi, both ^U and ^X become kill characters, both escapable with backslash.
