Well, it is just more or less the function `doc-view-next-line-or-next-page` (i.e. `C-n`) slightly adapted to djvu-mode, because djvu-mode works slightly differently.
It is meant for `djvu-image-mode-only` but I have simply bound it in the `djvu-read-mode-map` and it seems to handle things fine.
It is just a small addition that slightly improves the scrolling experience (i.e. it becomes like that in doc-view).
While I am here anyway, I have also created some code to implement `djvu-occur`
similar to `pdf-occur` (but synchronous instead of async) which works fine for most djvu documents. Also I have added some annotation drawing features.
I have created a new github repo for it
here. So if you are interested you could have a look at it or even test it.
However, I am not a very experienced elisp programmer, and although the `djvu-occur` code could probably could get merged without too much improvements, the code for annotation drawing can get cleaned up quite a bit.
Anyway, I am just informing you about it. I don't expect anyone to spend much time on it, as there is a good working pdf-tools already.
I am just playing with it a little, becauseI I think it would be great if djvu.el and pdf-tools.el functionality could all get merged into doc-view at some point.
But I fully understand that time and resources of volunteers generally are very limited and that it does not have too much priority anyway (as mentioned in djvu.el, djview already exists).
Okay, getting very much off topic here. In short, to me it seems that these scrolling functions handle cases consistently enough. Maybe they can be added as an option (and get documented as a not well-tested hack). If the code was on github/gitlab/etc, I would just have created an issue and there could be made a reference to the issue for people interested.