Earlier quoted context omitted.
I haven't worked out the specific numbers, but $60 billion is reasonable if you expect Uber to become a global near-monopoly on hired ride services and related logistical services they're branching out into. Whether that scenario is reasonable, is itself an open question, of course.
It seems divorced from reality to me, though I claim no real special expertise. They seem to have no more ability to be a monopoly than any other logistics or transportation powerhouse. The market cap of UPS is ~$90bn, and FedEx ~$40bn. And those companies have a lot of real actual assets* and (arguably) much stronger network effects than a local taxi replacement company. It's not that it's so implausible it couldn't…
In fairness, though, neither FedEx nor UPS count as a near-monopoly either, but the probability of a real one is correspondingly less probable anyway.