I guess "pure photography" might be something like William Henry Fox Talbot's idea of the "Pencil of Nature" – images drawn by nature with the photographer being just a servant to the sun. But I suspect that's not what we are talking about here.
If its retro we're after, lets go for some real innovation.
A button/switch on every camera that engages the sensor. If you forget to turn it on, you can shoot pictures the whole day, but not one will be recorded. And, while we're at it, let's make sure that the button "slips" once and awhile and even though you think you hit it, it won't record any pictures. That way we can resurrect the "pure" film experience of forgetting to check the rewind knob to verify that there is film in the camera and that the take up spool has actually engaged the film.
How about separating the ISO display from the actual ISO on the sensor, so that you have to select both. That way, you can recreate the "pure" experience of putting ASA 100 film in the camera and forgetting to change the meter dial from Tri X.
Or maybe, there can be a random feature where all the images on the card appear as though someone inadvertently opened the back of the camera without rewinding the film.
While were at it, let's extend the experience to Lightroom. Maybe every once and awhile when you upload your images, several of them will have chemical-like blotches on them or be undeveloped in the center, so you can recreate the "pure" experience of film sticking together on the developing reels.
Maybe have shots taken at ISO 100 have the same noise as ISO 100,000 to simulate the experience of someone developing the film using Dektol.
Better yet, sometimes the entire upload can be blank, simulating the experience of accidentally pouring in the fixer first.
I'll think I'll stick with today's photography instead of some retro "pure" experience.