It would be great to have an option on the screen button module to make its appearance more like a 'switch'. With simple 'on/off' item the button is hard to read. It would also be nice to allow 'inverting' the on/off on the display for a system that will be turned on with no redstone signal vs a system that can be turned on with redstone signal.

Here's a bad mockup left being current and the right being requested feature.

A Redstone Lever module would be very nice indeed

A workaround meanwhile is to use a Redstone Module that displays the current status (on vs off).

You are all aware that screen buttons can already be in 'toggle' mode right?

Yep, but I believe OP's opinion is that it can be hard to tell which state it's in at a glance.

I don't really have an opinion on the matter myself, although I might find being able to change the button's text based on the on/off status.

With the above pictures, it is hard to tell which state something is in. Especially when things can differ and be on or off with or without a Redstone signal. It would just be nice to have some more functionality if possible.

Currently it's hard to tell at a glance of a Screen if a button module is toggled. I love OPs suggestion, or new text fields that change text displayed on the button itself. One text field option for when button is not pressed, and one text field for when it is pressed.

Example:
'When not pressed' button text will read: "Off"
'When pressed' button text will read: "On"

Also an invert signal option would be really handy when controlling machines that are on by default.