Since the keyboard shortcuts Ctrl+L and Ctrl+R are already in use:
I suggest to use Ctrl+Shift+<letter key> or Ctrl+Alt+<letter key> for these actions, for example:Ctrl+L = Select for copying -> Left to Right
Ctrl+R = Select for copying -> Right to Left
Code: Select all
Ctrl+Shift+L Select all files set for copying from left to right
Ctrl+Shift+R Select all files set for copying from right to left
Ctrl+Shift+E Select all files marked as equal
Ctrl+Shift+U Select all files marked as unequal
Ctrl+Shift+N Select all files with no filter marker set
For convenience of mouse users, such actions could be bound to the direction-equality speed buttons,
e.g. a left mouse button click on "Equal files" (with "=" icon) button while Ctrl+Shift are pressed on keyboard would select all equal files. All such selection functions can by available also by right click mouse menu (maybe as a submenu of context menu that appears in Sync dirs' list of files).