active/default state/value handling to restore last known or default state values for certain running features like 'Beat Loop Size' & 'Beat Jump / Beat Loop Move Size ', and general support for 'hot-loops' loop memory length and locations metadata about mixxx HOT 1 OPEN

Thanks for this report.

I think, in order to keep issues manageable, we should move the keyboard aspect to a separate issue.
I'll comment on that anyway:

Also, there needs to be a cleaner way to manage user input context from the keyboard... for instance, if you are selected in the library with the mouse, you can then push spacebar to toggle big library, and generally interact with the keyboard shortcuts for other deck and mixer functions..... if you are in the search text box

... you can hit Esc in order to focus the tracks table (or root view of the feature currently selected in the sidebar).
And keyboard shortcuts will work.

Indeed the keyboard UX can be improved.

even if you go from text to blank faceplate of a mixer area

Yes, it may be unexpected that clicking a blank, supposedly unresponsive area doesn't not remove focus from the currently focused widget as it does in web pages or other apps.
This has been installed (#2307) to no not steal focus when clicking controls (buttons, sliders, ...) so we have a somewhat hazzle-free mixed mouse / keyboard / controller workflow (library navigation with controllers relies on focus and (emulated) keypresses). At that time we (I) didn't look into making exceptions for labels, widget groups (potentially blank space).
I tried to fix this a few time earlier, but didn't succed. Will give it another shot.

from mixxx.