I'm impressed how much effort you put into these layouts. I just started my own variant and it takes quite a while.
EDIT: Okay, you don't need to sacrifice Shift or Tab! Here she is!
http://www.keyboard-layout-editor.com/#/layouts/d8cf627251459c7853f7f09b279b424c
The main thing I wanted is to get double-width space, and also to free the pyra key to be used only for menu.
With this layout all the orange symbols are accessed via the "FN" key instead of the Pyra key.
What do you think?
Not bad, but I still don't see the advantage of a double-width space. If you can't hit a single-width key with your thumb, thumb typing is not going to work anyway.
Fn as a key in the main block (like on the Pandora) is not needed imo if we already have Fn as a shoulder button. Why an Fn key that is easy to press but not a Ctrl or Alt?
Sacrificing the dedicated slash and dash keys just to get a slightly easier to press space and Fn, that's not a very good trade-off in my opinion. But of course preferences can differ on this.
Well the FN key gets used for a lot of punctuation so it makes sense to me to have it labeled on the main keyboard section. I never got used to shoulder buttons for modifiers and I never use Ctrl or Alt on the Pandora, so I am fine with them on shoulder buttons.
The Fn key being used for a lot of punctuation as an argument to dedicate a main block key to it, is a kind of cyclic argument.
In my layout, all of the punctuation needed for normal text is available without Fn: , . ; : ' " - + / ? ! ( & ). You only need Fn for symbols that do not occur in normal text: \ | [ ] { } < = > ` ~.
In your layout, you sacrifice two moderately important punctuation keys (to make room for bigger space and Fn), so now you need Fn for ' " / ?, and then you use the fact that you need Fn for punctuation as a justification for having Fn in the main block.
Regardless of whether you got used to it on the Pandora or not, shoulder buttons are a perfect match for modifier keys. Modifier keys are keys you have to hold down while pressing other keys. For the non-shoulder modifier keys, there are three options:
1. you have two keys per modifier (one on each side) to make all combinations easy to do
2. you put the modifier in the column between the nubs, so it can be reached by both thumbs (though not comfortably)
3. you have only one of them, and make it sticky (like the Fn on the Pandora or the Shift on a typical touch screen keyboard)
Option 1 is not really an option because it wastes too many keys. Option 2 works, but it's not very comfortable for modifiers you really need a lot (i.e. Shift). Option 3 works, but it will only be worthwhile when you don't use the shoulder buttons (e.g. because you put the device on a table). Sticky means you do two sequential thumb presses instead of two more or less simultaneous ones. When the same thumb is needed for both presses (e.g. when Shift is on the right and you want to write a capital P), it's not very efficient.
Anyway, my point is: I don't think it's useful to put
any modifier in the main block. I put Shift there in my proposal mostly because there's only room for three modifiers in the column between the nubs, and because it can act as a dedicated compose key or some other extra key.