The Brownie six was the obvious choice because of the space it offered for the components, but having looked at my camera collection, I see no reason why this concept even with a bit more functionality would not be perfectly possible. I had some thoughts on that.
The next easiest option would be to use a leaf shutter which are mostly located in the lens and not at the back. In a typical 35mm body, the spaces for the film canister and spool offer more than enough space to place a battery and a small ESP32 board with the necessary components.
I would discourage using curtain shutters cameras as these are easily damaged, but even with metal blinds, the backing plate present in most SLR's and rangefinders would probably have to be removed for the light sensor to clear the shutter. In many cases this would be a destructive mod. Another potential suitable body for this mod would be something like an Agfa Clack.
Adding a second roller switch would enable for 3 commands to be sent. For the Brownie this does not make a lot of sense, but for an SLR, rangefinder or simple point and click camera with a viewer at the back, this would be perfectly reasonable.
Shutter speeds that work will depend on the lens type and lighting conditions, but with some crude experimentation, I found that under normal lighting conditions an eps8266 was fast enough to catch the signal from the light sensor within 125th of a second most of the time. In slightly darker settings 500 works pretty good as did "bulb" on various cameras. I the end you can go as slow as you want to make it work because it does not really matter for the end result! It is more about the sound that you want from the camera if anything.
On a separate note, I have seen a lot of nice new entries in the competition using ESP32 BLE modules. Got a lot of inspiration from those and perhaps the ESP32 is my new favourite controller!