The idea starts with the Planck Light. We take this keyboard with it's low-profile switches and keys and hyper minimalist/slim design. Then, we make changes to the design.
First, we change it from a MIT layout to a grid layout. We don't have an orientation problem because of the color of the keycaps are different on the bottom row and outer left and right columns. Now the thumbs can do their thing as modifier keys (space as well).
Now for the "big idea": changing the key caps: What if each key cap had capacitive touch sensors which can communicate to the board. As you lay your fingers on the home row, this communicates to the QMK firmware that you're in the default layer. Once you shift all four of your fingers up a row entirely (left hand on QWER and right hand on UIOP), then this will change the layer to of the keyboard, enabling an entirely new layer. If you shift down from the home row, (left hand on ZXCV and right hand on M,./), then you enable another layer. By shifting positions of your resting place, you switch layers! This is why it's call the Planck Shift.
The F and J keys should have notches for tactile feedback that your fingers are in the right place for the default layer. As you shift your hands up and down, you're immediately switching modes and you're getting feedback from the feeling of the keys (whether the pointer fingers feel a notch or not) to know whether you're in one mode or another. Modal experiences brake if they require the user to mentally track the mode they're in; UX should provide feedback, whether visual, audial, or tactile.
With this setup, the ability to customize this keyboard really is great. One idea is to have the top layer (shift your fingers up), to act as the number keys. The bottom layer could access a lot of special characters and navigation. What's great is while in the top and bottom layers, the nearby keys from where you're fingers rest can also change; so the keys below the numbers could be a lot of different special symbols (!@#$%^&*(), or even ⁄€‹›ﬁﬂ‡°·‚).
While in the default layer, the bottom most row is available for the the thumbs to act as modifier keys (ctrl, alt, os, shift) as well as perhaps a space character. When shifting up or down, these could still remain as modifiers for the thumb (most-likely for the up-layer), or non-modifier keys (most likely for the bottom-layer).
In addition to the capacitive touch, the keycaps could also had black/white e-ink displays which could change the letter displayed on the keys as well as the foreground/background color (black background with white foreground, or white background with black foreground). This black/white capacitive keycap design could turn your keyboard into a minimalist, fully customizable keyboard all via software, both functionally and visually!