What voltage for the all-DC house?

You do not want to distribute low-voltage power through in-houe wiring like the ones normally used when connected to the network.

Low voltage wiring is perfectly viable, but it requires shorter paths, what require rethinking where it runs trough, where appliances are located, and where you have outlets. It means losing some freedom, so it is not something people opt-in, but a down-side of other choices people may want to make.

And if you did one of those choices, you will have the voltage forced onto you already, so no point asking.