Take nice housing in a nice town in a nice location (good climate, pleasant nature, far from the industrial complexes churning out the post-scarcity goods, good culture which takes time to build). Who gets to live there and why? Who gets to travel there to spend a few weeks of their year? These are not all identical - some are more desired by more people to make them more scarce. So you naturally have scarcity.
Furthermore, the current production levels and resource management depend on productivity. And productivity depends on incentives. Take away the incentives (in an absolute 'sharing economy' you speak of), and suddenly you will have an increase of scarcity in places where you thought scarcity to have been solved.