When I think about all the bad pictures I took while shooting film, I shudder to think of the pretensions I had of being a "great" photographer.
Somehow, the ability to see the image on a flat screen (as if viewing a print) transformed my ability to make better pictures. I noticed it immediately with my very first digital camera, an Olympus D-550, which had a rear view screen literally about the sized of a large postage stamp. It transformed my workflow, too; everything was faster, better, less expensive in terms of providing images to illustrate my stories as a freelance writer. There is no way that I would want to go back.
Having said that, from a conceptual level, I think that the only "sensible" approach to "digitizing" film cameras would be to have a drop-in module the shape and size of 35mm film cartridge. The cartridge would contain the battery, storage, and electronics to make the thing work. A "tongue" sticking out of the cartridge -- like the piece of film that you would pull across the film plane of a film 35mm -- would contain the sensor. You drop the thing into your old film 35mm, flip a switch on the side of the cartridge, close the back, and shoot pictures. You can't preview (other than through your camera's OVF, you can't chimp (review pictures you've taken), and the only way you can see your pictures is when you transfer them from the cartridge/module via cable to your tablet/laptop.
You have replicated the film shooting experience in all aspects except you are generating digital files, and you don't have to develop your film or wait for it to come back from the drugstore. I think the electronics are small enough now that this could probably be accomplished.
Whaddya think?
Cheers, Jock