Support for multiple levels of sidebars
I think it'd be nice if flexdashboard could support global and local sidebars simultaneously. This way a user could define inputs in the global sidebar that should apply to all pages (say geographic filters) and also have inputs defined at the page level.
Actually, given flexdashboard's global -> menu -> page hierarchy it might be nice to support 3 levels of sidebars so that there would be an intermediate sidebar for all pages under a menu item.
I'm struggling with implementing something elegant myself. I don't see a good way to insert conditionalPanels into the global sidebar (conditional on current page or page-group).
There are global and local sidebars, but it seems you have to pick one. If you try to combine them, the two sidebars end up overlapping.

---
title: "Sidebar for Multiple Pages"
output: flexdashboard::flex_dashboard
---
Sidebar {.sidebar}
=====================================
Global sidebar
Column
-------------------------------------
Page 1
=====================================
Page 1 Sidebar {.sidebar}
-------------------------------------
Page 1 Sidebar
Column
-------------------------------------
### Chart 1
Chart 1
Page 2
=====================================
Page 2 Sidebar {.sidebar}
-------------------------------------
Page 2 Sidebar
Column
-------------------------------------
### Chart 2
Chart 2