I never thought I'd say this but: I think most worthwhile public domain content is now in e-Sword format!
BibleSupport.com claims to have 5,218 resources for e-Sword 10.x. There are at least 5,000 resources for e-Sword, that are legally distributable, but are not available from BibleSupport.com. Round that off to 10,000 resources.
QuickVerse 2013 Platinum Plus claims 574 Volumes. Depending upon your POV, I'm either being very mean, or very generous, in assuming that QuickVerse 2012 has the same number of STEP resources. Findex counted resources in its packages, the same that Libronix counts resources in its packages.
Logos 5 Portofolio Edition contains 2,585 resources. ( https://www.logos.com/comparison . That page defaults to Logos Gold Edition, Click on the link for Portfolio Edition, to see the details.)
The Maryland State Department of Education requires schools have a library collection of at least 12,000 items. A middle school collection is expected to have 15,000 items, whilst a high school collection is expected to have at least 18,000 items. (http://articles.herald-mail.com/2008-04-14/news/25088737_1_library-collection-collection-size-school-year ).
Resources for e-Sword, and Logos are counted differently. If resources were counted the same, then Logos Gold Edition (1,100 resources) is the more appropriate comparison. The school library counts individual volumes, which is what e-Sword does, rather than sets of volumes, which is what Logos does.
Using Logos 5 Platinum Edition as one's starting point, it is fairly easy for one's Logos Library to be the size of a Maryland High School Library. (I am deliberately excluding the damage to one's wallet, in the definition of "easy". If one wishes to have 18,000 volumes, with minimal impact on one's wallet, download the books from The Internet Archive Archive.org, and Project Gutenberg Gutenberg.org .)
For e-Sword 10.x, getting to the minimum Maryland School library size (12,000 volumes), is doable, if STEP resources are actively sought out. Getting to Maryland High School library size (18,000 volumes) requires one to be creating resources.
In terms of "worthwhile public domain resources", the most obvious lack, for e-Sword, is in Greek and Latin material. More specifically, the complete corpus of the church councils, Papal bulls, Papal briefs, and encyclicals.
The second major omission is apocrypha and pseudepigrapha material. More specifically:
- The texts that made it into the Bible, and then were removed: For example, 3 Corinthians;
- The texts that almost made it into the Bible: For example, Shepherd of Hermas, Acts of Paul;
- The texts that did not make it into the Bible: For example, 4 Baruch, 5 Maccabees;
- Book of Common Prayer (USA) (1976);
- The Scottish Communion service of 1764;
- Texts that explain the liturgy, such as James Davis' Manual of the Book of Common Prayer;
- Protestant liturgies, such as A Book of Common Order;
- Catholic Liturgies, such as Tridentine Missae;
- Orthodox Christianity;
- Oriental Christianity;
- Celtic Christianity;
Consequently, I disagree that most worthwhile public domain content is now in e-Sword format.