Ask HN: Is there any startup out there building airliner planes?

Airliners haven't evolved much since 1960 (unless you count fly-by-wire and vastly improved fuel economy...) for a reason: the current designs are fit for purpose, development is incredibly expensive and prospective clients are - for good reason - conservative buyers.

The closest thing to a viable airline startup is probably Mitsubishi Aircraft Corporation, effectively a joint venture between huge conglomerates with existing experience in aircraft component manufacture and leasing. The aircraft they're due to roll out soon may well be a commercial failure.

At that level of capitalization and complexity, military aviation would almost certainly offer a better chance of success...that's probably where SpaceX's hockey stick will lie over the long term.

Light Sport Aircraft and experimental/kit airplanes, sure (although "startup" is probably the wrong word for it).