The construction of the first commercial space ship.
It's clever. The design of the launch vehicle uses many common parts with the spaceship, so there's been a lot of testing done at both component and subsystem level already. There's some penalty in terms of things being over-designed for their purpose, but that's liable to be far more than compensated for by knowing that the spacegoing stuff already works over the majority of the flight regime.
One thing that surprised me - how roomy it is inside. Obviously it's weight rather than volume limited.