The huge appeal of the HHKB to most is the Ctrl and Backspace positioning. Once I got used to it (particularly Backspace) I started reprogramming my other boards to mimic the layout.
I've been using primarily Macs for the last 20 years. Ctrl is an almost un-used key on the Mac. It's only used in the command line, and most people (including me) don't use the command line all that heavily. Our primary key for application shortcuts is Command (⌘), which is found to the immediate left and right of the space bar. Having a Command key on the right is important, because all the standard app shortcuts are on the left side of the keyboard. They are ⌘-Q (quit), ⌘-W (close window), ⌘-S (save), ⌘-Z (undo), ⌘-X (cut), ⌘-C (copy), ⌘-V (paste). Trying to hit the ⌘ key with the same hand as the shortcut key would be awkward. Just like we use a Shift key with one hand to capitalize letters on the
other hand, you want to use your right hand on ⌘ while pressing the shortcut key with your left. Of course there can be shortcut keys all over the map, so it's nice to have Control-Option-Command on the left and Command-Option-Control on the right. They are clustered all together (and under the Shift keys too), so it's easy to chord any combination of these keys, and you can do it with either hand to easily hit shortcuts on either side of the keyboard. This is such a versatile, logical and natural system that I can only shake my head in dismay when I look at something like HHKB. What in the world were they thinking?
Now I am in the process of moving to Ubuntu, but I find Mac keyboards work very well on Linux. All I have to do is enter my keyboard layout options and swap the position of the Ctrl and "Win" keys. Then I've got a nice familiar layout of Super-Alt-Ctrl on the left and Ctrl-Alt-Super on the right. Ctrl does the same functions on Linux that Command does on a Mac. Super/Win is basically unused by Linux, but I can configure all my personal shortcuts to use it, to switch workspaces, toggle fullscreen or minimize windows, without any worry about it conflicting with anything else in the system. Again it's all logical and convenient, and it would all be harder on a HHKB.
As far as backspace is concerned, backspace belongs on the left half of a split spacebar. For many years it has seemed obvious to me that all spacebars should be split, and backspace should be on the left. It's not a new innovation either. Erase-Ease™ keyboards were introduced in the 1990s. Unfortunately, they were also trademarked and
patented(!) at that time, which I believe is the only reason they didn't quickly take over. The patent didn't expire until 2016, so maybe now this idea can finally start to make a comeback.
And here is what I'm building today →
http://www.keyboard-layout-editor.com/#/gists/53eb271326a5e7a951cf8778208e9b5e