I don't think optogenetics is feasible for human BCI. Optogenetics requires one to express channelrhodopsin proteins in the neurons of interest - which means you need to genetically modify the human at birth. We know how to do this in mice, but not humans since the gene expression pathway for neural proteins in humans is poorly understood (unlike mice and zebrafish). Even with optimal designer baby scenarios, there's no hope for us adults; gene-editing therapies for adults is way harder and we'll likely be long dead before we see anything close.