I agree that mitoTALENs look promising, as does some early work on delivering RNA to mitochondria so that the necessary proteins get made even in the absence of genes. That said, I'd have said the same about exploiting mechanisms in leishmania [1] to deliver useful molecules to mitochondria if you'd asked me five years ago. That line of work seems to be in the doldrums too at this point, not much progress to be seen.
The most promising sign is the metasign - that we can compare and contrast so many different approaches, and complain because some are not getting more attention. Yet overall things are happening.