I can draw a vertical line with the ‘barline’ line-body-style but positioning it exactly is fiddly, and the positioning is undone by the slightest note-spacing change.
What’s the purpose of the line that joins the staves at that point? Is it to indicate some kind of synchronisation or coordination between them? If so, we have plans to add a dedicated feature for this kind of line in a future version of the software.
No, that’s not in our plans. Once we have a feature for more general coordination lines, you’ll be able to set that to look like a regular barline if you wish.