I set the next-layer of my alphabetic characters to go back to the main layer, and made sure that numeric and math characters stayed on the same layer. This produces some of the desired effect of disabling the Shift after typing, but not the caps-lock.
Touch Keyman does not (AFAIK) currently have a built-in way of emulating Caps Lock yet, but as you suggest, a determined developer could create a CAPS layer without next-layer options.
- Tap Shift once, and we go to the SHIFT Layer.
- If you type a letter, it goes back to the normal layer after output (next-layer).
- If you tap shift again, if goes to a custom CAPS layer (next-layer always undefined for letters).
- Typing any letter would give the capital, and stay on this layer.
- Tapping shift from this CAPS layer would take you back to the normal layer.
One caveat is that on some keyboards (like AZERTY), SHIFT and CAPS may be different for non-alphabetic characters.
This could be done, but @Marc may suggest that we wait for Caps to be truly added as a feature.