Here is an example, showing just how impractical I am, in what I would consider an "ideal keyboard" that could be manufactured by Unicomp:
This is a 121-key keyboard. This should be something they can make physically with their existing tooling, since 122-key keyboards by IBM, at least, provided for putting the 101-key ANSI-style main typing area in the center instead of the 102-key ISO-style main typing area there, even if this was never used.
The first keyboard image in the diagram shows how it would look if it were used as a 122-key terminal emulation keyboard. The big problem, of course, is the missing key!
In that case, one option would be to use the |\ key above the ENTER key (now the CR key) as an Fn key. Fn-A might be the {} key, Fn-S might be the <> key, and Fn-Q might be {, and Fn-W might be <, to prevent having to use Shift-Fn combinations. With only two keys at once, there shouldn't be ghosting. (There is now a diagram in the upper right, showing the Fn key in green, the two unshifted keys in blue, and the two shifted keys in red.)
There would really be two modes provided for on the custom controller I envision for this arrangement - one that uses terminal keyboard scan codes, like the IBM Host Connected Keyboard, and one that behaves like the PC/5250 or the Boscom.
The second keyboard illustrated is the mode used for conventional typing. Here, there are those 10 unused keys to the left, three of which are used to replace the Print Screen, Scroll Lock, and Break keys. Here, there's no reason, with all those extra keys, to use the |\ key as a Fn key. The other seven keys could be used for things like Windows Shift, Windows Menu, and the extra international key. (A small diagram in the upper right now shows how this could be arranged: Fn in the F1 position, the international key in the F7 position, Windows Menu and left Windows Shift in the F9 and F10 positions respectively.)
The third keyboard in the diagram illustrates an exotic arrangement that would probably be little used, but which I've thrown in for completeness. Here, the Print Screen, Scroll Lock, and Pause functionality is taken care of by setting up the numeric keypad exactly as it was on the 84-key IBM AT keyboard. And so the ten keys on the left now serve as duplicate function keys in the old arrangement! (Now, the keys involved are outlined in blue. As the right Ctrl and Alt keys are prefixed by E0, and are not simple, they're in red in the inset diagram, and a possible candidate for a function key in this mode is shown in green.)
EDIT: And, come to think of it, if F13 through F24 are used for multimedia keys in the modes other than the 122-key emulation mode, then one could use F13 for "help", F21 through F24 as the four multimedia keys, and have the ten keys on the left available... to use the keyboard on a Sun. That, and the availability of a mode for Macintosh use would make the keyboard truly universal.
EDIT: Oh, dear. The benefit of the third arrangement is to allow games to treat all the 84 keys that were on the AT keyboard as so many push buttons.
One of the things that might be done with them is to simulate a piano keyboard... but to do that you need NKRO. The AT keyboard was a model F, however, so it could do that.
While there was a 122-key Model F keyboard from IBM, it's not as if Unicomp likely has the dies for that kicking around. (And they would have to make a change to add the num lock/caps lock/scroll lock lights, which they do have on their existing 122-key Model M keyboards.)
So what I thought only required a custom controller is, in fact, like asking for the moon.
