show scale bar or number to indicate the number of bases in the visible region

This is useful. Looking at the coordinate bar to get an idea of how many bases you have in the view gets annoying. And for figures for publication, where every pixel of space matters, you may want to remove the coordinate bar (I suppose it can be Photoshop-ed out) and use scale bar to convey dimension information more tersely, but the scale bar should be rendered by JBrowse. You should be able to toggle the scale bar on/off from the client.