It would be a useful enhancement to uniq to replace all lines
considered non-uniq (i.e. those that would be removed from the output)
with a message about how many times the previous line was repeated.

I.e.

$ cat <<EOF | uniq --replace-with-message '[previous line repeated %d times]'
first line
second line
repeated line
repeated line
repeated line
repeated line
repeated line
third line
EOF
first line
second line
repeated line
[previous line repeated 4 times]
third
line

Cheers,
b.