YC companies can post on the jobs board (https://news.ycombinator.com/jobs). Job postings automatically go to the frontpage and don't have any upvote system
Any suitably complex problem space can be 'sexy' if you consider it in abstract terms. It doesn't matter if you're solving how to move crates on ships, or move people in cars, or move streams of data in networks - it can all be a lot of fun irrespective of the end result. The main differences are the constraints on the problems, not the problems themselves.