I can't think of anything before the E-series that could be considered a still-image, digital output, SLR camera in design.
There were various industrial, scientific and medical digital output cameras that were around well before the E-series, but they couldn't be considered SLR cameras. Some were out there that approached the SLR design point, but weren't digital output, being modified analog video cameras with an analog output.
One fact, though, is that they did not work all that well. Kodak's approach worked better once they leveraged the sensor size to where it was close in size to the size of the film it was replacing.
Of course, the successor to the E-series, the D-series, followed the same approach, as has everything since. I do believe that it was the Nikon/Fuji E-series that woke the rest of the camera world up to the idea that the DSLR idea was a good one.