Blind Accessibility - disable ALL visuals with a keystroke?

Is this possible?

I am creating a game that is playable by sighted and blind gamers alike without any means of text to speech or external accessibility; all my accessibility is internal, through game mechanics.

The problem is that a lot of blind gamers are running very old machines, because they have no need to update graphics cards, or processors which are often needed to help with graphics.

A lot of my playtesters can’t run the game, even on the lowest possible scalability setting. Does anyone know how to completely remove ALL strain on the visual processor by a menu setting or ingame keystroke?

Only easy cheaty way I can think of doing it is to have a keypress that runs something like r.ScreenPercentage 1, which should in theory down-res everything to 1% of its current resolution. But I’ve never tried it and it may end badly.