GUIs should be fully keyboard-driven

The way we are moving I believe soon we will be talking to the websites not just clicking or typing around...

Yes. One problem with this argument in particular is that every TUI reinvents the wheel and designs its own schema.

To reinforce author's point, classic GUI frameworks and their guidelines actually provide hotkey schemas for common actions by default, and hot paths for quick interface traversal. They're universal and work by default, so in a lot of cases you don't even need to think about it, only extend it with your own actions. Absolutely nothing prevents you from doing the same in a TUI framework, but at this point the supposed simplicity and flexibility is lost.

New GUIs have other innovations, see for example Microsoft Ribbon that adopted link navigation from Vimperator to make classic toolbars discoverable, compact, accessible from the keyboard, and customizable - all at the same time! Unthinkable for any other UI paradigm.

It's incredible that after the Electron devastation era this unification and keyboard accessibility feels like some kind of lost art, and the perceived lack of keyboard driven GUIs is used a strawman to criticize GUI as a principle. Status quo of "most apps do X" is not the principle. It's also not true, essentially all good GUI apps are keyboard driven, and surely most professional/heavy user ones.

Design good interfaces, not bad ones, regardless of the paradigm. This is harder than it seems, and TUI is not a automatic substitute for your lack of this skill. If you think it is you will design a bad app, in the same way pixel art looks hideous when used to compensate for game designer's laziness. In fact, a lot of recent TUI apps I see are pure terminal cargo cult and are simply worse by being TUIs.

Your resource mostly describes how to make keyboard-based workflows accessible. But just because the full functionality of an app is keyboard accessible, doesn't mean that it works as well as the pointer-based approach - especially if you have an app with multiple menus, sidebars, headers, footers etc. Maybe you could tab through everything, but a pointer will be faster. This is where a "keyboard-first UX concept" is missing (from GP).

I think an interesting idea to solve this would be a "focus navigation mode". Enter this mode with 1 shortcut and then navigate between items with a few keys; like a combination of mnemonics and screen reader navigation e.g. jump between headers with "h" etc.

Which ones, besides web frameworks pretending to be desktop ones? Most if not all frameworks I know support keyboard navigation.