Seems to me that if Tesla can bundle things from companies/divisions they own it may work out well for them. Driving a Tesla? Bring it home and plug it in to pull power from your PowerWall, which was charged during the day by your SolarCity panels. Charge a little less on the secondary items, but increase your volume by trying to drive sales to Tesla vehicle owners who might otherwise have never considered such a thing.
If they can combine the PowerWall with the vehicle charging station, that just makes it better.
I think the major problem is the total lack of synergy between Tesla and SCTY.
Tesla has a sales program which is basically 0 marketing, 0 sales, 100% inbound and SCTY is tele-sales + door to door (which is payroll intensive and harder to manager). Tesla has an operations cycle which is completely centralized except for the car delivery. All of SCTY is contractors installing stuff on customer roofs.
I do not see any operational synergies between the two companies except for the superchargers (and buying SCTY for superchargers feels wrong).
What the press release talks about is combined installation of solar panels and Tesla home infrastructure (charging station + Powerwall). I think that speaks to the sales perspective too - it could be very easy to upsell the (incoming) Tesla customer to a Tesla + SolarCity installation, for a lower CAC than the usual SolarCity sale.
If they can combine the PowerWall with the vehicle charging station, that just makes it better.