Since you can transfer from belt to belt with inserters, wouldn't it make sense to have that visualized as well? Especially in certain modpacks (pymods) where you don't have splitters for quite a while this could be very useful.

Currently there is no way to read what inserters drop onto a belt from the belt's API, so I would have to search the world manually, which is quite expensive. If that API feature ever gets introduced I will certainly implement it though.

I see, especially with adjustable inserters this would be pretty painful. Is there already a feature request in the factorio forums?

I don't believe it is, at least I haven't asked for it specifically since it wasn't in the scope of the mod.

Asked in the forums: https://forums.factorio.com/viewtopic.php?f=34&t=104641
Maybe someone has some insights.