World ships are hypothetical, large, self-contained spacecraft for crewed interstellar travel, taking centuries to reach other stars. Due to their crewed nature, size and long trip times, the feasibility of world ships faces an additional set of challenges compared to interstellar probes. Despite their emergence in the 1980s, most of these topics remain unexplored. This article revisits some of the key feasibility issues of world ships. First, definitions of world ships from the literature are revisited and the notion of world ship positioned with respect to similar concepts such as generation ships. Second, the key question of population size is revisited in light of recent results from the literature. Third, socio-technical and economic feasibility issues are evaluated. Finally, world ships are compared to potential alternative modes of crewed interstellar travel. Key roadblocks for world ships are the large amount of required resources, shifting its economic feasibility beyond the year 2300 and the development of a maintenance system capable of detecting, replacing, and repairing several components per second. The emergence of alternative, less costly modes of crewed interstellar travel at an earlier point in time might render world ships obsolete.