You know Weapon feats, Skill Feats, Mass Combat rules, ect... we're supposed to go in that space, but they were popular enough, and they didn't have the time to fix them, or the staff, or the money, so they grew desperate and decided on the names as filler, but they way over did it, they should have come up with a few other ideas.
Here are five easy, none game breaking things they could filled those 17 pages with that would have been better and more interesting.
1. Every Deity in official D&D that has ever existed, including the obscure ones, including domains and home planes info. No one would have to go without their favourite God again.
2. Warlock Patrons in table form by Patron type.
3. Basic mechanics for other settings, Warforged, Lender, Defiling rules, and so on. I know the books for other settings are never going to happen, this makes that glaringly obvious, but you could have given them the mechanical elements at least, like races and key setting mechanics.
4. Convert 4e fighter/ranger/rogue/warlord at will powers into 5e feats, once you figure out the first one, the rest would be easy.
5. Fluff for the Subclasses. Where are the best places to find Shadow Magic Sorcerors, what academies teach War Magic, Divine Souls are common in the Old, Empires, Samurai and Kenzai are native to Kara Tur and can be found often in these places, The Celestial can be used in Darksun thusly, and so on.
I mean seriously, gathering those names was an hour of work.