9) Light proton pump
There has been extensive research on bacteriorhodopsin, which is very similar to cruxrhodopsin found in our species. There are very few sources on cruxrhodopsin specifically though.
I did find one very interesting article about Haloarcula japonica archaea about cruxrhodopsin. Expression of this gene was regulated by the presence of light, and low oxygen tension. Which I think would be really interesting to look for sensory mechanisms in the genome and gene regulation and see how respiration and the proton pump are connected, and maybe find more questions about ATP formation with the proton pump.
I think it would also be good to see if there are any significant differences between bacteriorhodopsin and cruxrhodopsin.
This paper (Coordinate regulation of energy transduction modules in Halobacterium sp. analyzed by a global systems approach) on H. salinarum has a lot of information on specific mechanisms of light proton pump action and how this organism moves between modes of energy harvesting.