On our development wiki just now I moved [[WPX:List 1]] to [[WPX:WikiProject Test/List 1]] to make it part of the WikiProject. However, doing this does not cause the page to inherit the table of contents. Also, wikitext-type pages do not inherit the table of contents either.
Pages that are part of the WikiProject should consistently inherit the table of contents. It should not require additional effort from users.