It's essentially the same mechanism: the terminology is immediately understood. The market is public opinion, in a rather special public. If these people all 'short' Uber, it might not even go public. I guess the equivalent would be trying to take all the VC money back? And obviously the equivalent to a long position would be investing more VC money in Uber.

Nobody would seriously argue that there's no difference between the two because Uber doesn't exist yet in 'stock' terms. They need to translate the initial investor enthusiasm into an IPO, so short/long spells out the likely climate for said IPO.