Will we be able to drill down in graphs any time soon? The same way you can have hierarchies in most other visualization tools, eg Qlik, Power BI
Drill-down graphs in shiny have been possible for quite some time. Compared to these other tools, using shiny to implement drill-down does currently require more effort and thinking from the developer, but in my mind, that extra effort is well worth it, because you can do way more with it once you understand it.
For example, here's how to implement various drill-down graphs with shiny and plotly. The reactive programming concepts that power those examples translate to any shiny output widget (e.g., ggplot2, base, leaflet, rbokeh, DT, etc), not just plotly. That gives you essentially limitless potential in terms of what types of graphs you want to put into a drill-down as well as how you want to share that information across multiple views.