I was thinking about the idea of hybrid optical viewfinders this morning, and trying to figure out why none of the large DSLR manufactures have started to use the transparent LCD's in the optical viewfinder more effectively. Keep in mind that I am not talking about an electric viewfinder, just using the technology to give the user more information in the viewfinder. Currently Nikon does use this somewhat, for the low battery warning and grid lines for example, but there are way more possibilities.
Here are the possibilities that could be unlocked by further use of this technology:
1. Live histogram in the viewfinder
2. Display blocked shadows and blown out areas, the Matrix meter already knows this, so there could be a way of showing this to the user. The LCD could simply blink or display "+" symbols in blow out areas and "-" in blocked shadows.
3. Movable grid lines and rule of thirds, gold rule etc, not the fixed ones we have now.
4. A form of Quick menu, aka "i" menu or My Menu.
5. Battery status (% charge, not bars like the top LCD)
If Nikon was to use transparent LCD's to display information in the optical viewfinder, how much would you like to see? Should the information simply be black? Should colour information be shown, or would that be too distracting? Would you want this at all? It could easily be cycled or turned off like the rear LCD, so there aren't many downsides really.
If I take a good photo it's not my camera's fault.