Wasn't this basically expected/intended/inevitable? Considering Musk was one of the founders, along with his cousins that currently run it.
Are you implying nepotism? Would you have said that it was "basically expected" if neither Musk nor his cousins would have been involved in SolarCity?
I'm never sure how I'm supposed to interpret "on paper". Purely on current financials? That seems a poor way to plan IMO. There seem to be quite a few ways to market to each others customers and provide a more comprehensive "package" with this deal. I imagine we'll see car + powerwall + solar packages marketed directly soon.