I would love to take feature requests, but it's honestly not maintained. Don't get me wrong, it wouldn't be hard to reintegrate it with the current release, but I believe the idea should be at least approximated with vimscripts rather than making someone build a custom vim release to support this feature alone. Plus, now :rnu sort-of mimics this functionality by showing the current line number on the 0th row, instead of '0'.
On a side note, to your second request of left-side/right-side splits for line numbers: my first experimentation was to do just that. Left side was rnu and right side was nu, but the way vim's buffers work out, it wasn't very practical. It also caused headaches for rtl text and so on if I remember correctly.
On a side note, to your second request of left-side/right-side splits for line numbers: my first experimentation was to do just that. Left side was rnu and right side was nu, but the way vim's buffers work out, it wasn't very practical. It also caused headaches for rtl text and so on if I remember correctly.