The Page break template provides some basic formatting support for works on Wikisource, but it's implemented differently on different wikis and some Wikisources don't have it at all. It seems like it would be a good idea to make this a built-in feature of Wikisource by turning it into a parser function, perhaps in the Proofread Page extension or another extension used specifically by Wikisource.

Note that this also affects Wikisource exporting since (on English Wikisource at least) the template includes CSS hints for breaking pages in e-books.