alt Hacker NewsPart of the delay was also the 48V architecture. So in addition to the obvious new things like stainless steel panels they also had to redesign mundane parts like window motors and interior lighting. The Cybercab is also using a 48V architecture so even though they've never talked about it being an R&D platform maybe they'll retcon it that way.
That forces a redesign of all the car electronics. While it might well be a good idea anyway from an R&D point of view it's undeniably expensive.
(I have a very slight visibility on 48V car audio R&D, for example. Most digital electronics could be adapted with a different DC-DC converter but the audio power amp stage takes direct supply voltage)