The Cyclopedia is probably the better comparison, formatting wise. And you will notice that the 5e DMG ToC does mention siege weapons...
Sorry, I reserve the right to feel as disappointed as I choose. We'll see how much technology infiltrates into the standard game.
I do not ever remember him mentioning gestalt characters. Do you have a link to that?
Firearms, my thoughts.
For those disappointed by how few pages in the DMG are dedicated to optional rules/modules, I think a little perspective is in order. The Dungeon Master's Workshop chapter has 26 pages (25 if you assume a full art page at the front of the chapter). If you look at the PHB, the ENTIRE rules of the game (chapters 7-9) is covered in 27 pages (24 if you don't count the full art pages at the front of each chapter). So there are more pages in the DMG dedicated to rules options than there are pages in the PHB dedicated to the actual rules of the game. And this doesn't even factor in the possibility that there are sidebars with optional rules in other sections of the DMG. For someone craving rules options/modules, I for one am not disappointed in the least.
I took a quick look at the battlesystem rules in AD&D. I really don't think you'll see anything similar in the DMG.
With that said, there is another set of rules that appeared in the BECMI rule set called War Machine (X10). That set of rules took about 3-4 pages in one of the modules. We might see something like that, but it would have to be a little more scaled down.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.