Hi,
i really like the idea of using alpha-keys as modifiers. I got this idea a few days ago and i think this could be a huge improvement.
But there are some points i got stuck on:
You won't be able to hold an alpha-key to do things like thisssssssssss, but i don't think this is a problem for letter keys. Space, return, backspace, arrow keys, ... should be able to generate multiple keypress events when you hold them.
If you want to detect if a key is used as a key or a modifier, you have to look at the key release event. In your example, the software would't be able to type the letter A when the key is pressed, because it can't determine if it is used as a key or a modifier. Having the software typing the key when you release the key will generate an input lag. I don't know how annoying this is or if you can get used to it.
Can you post some details of your desired layers? How are the Num and Nav-Layers are looking? Would be great.
Returning to your question:
I've bought a used Tipro a week ago (
http://www.ebay.de/itm/Kassen-Apotheker ... 3f31a0569e) and already tried the programming software. You can define key mappings for four different layers, but the software is not flexible enough to do things like reacting on a key release or mapping key combinations to single keys.
I don't know anything about the Access-IS...
Of course you can get the full flexibility if you build a custom keyboard and program the keyboard controller the way you want it, but i think that would be too much for prototyping a new keyboard layout.
Did you think about writing a software running on your computer that does the remapping? You would have to install it on every computer you're working on to use the layout, but it wouldn't be dependent on the keyboard you're using.
AFAIK there is no programming language available that could do this platform-independently, but i know that there's a scripting language for windows called AutoHotkey that is designed to do key remappings and stuff like this.