Canon has filed a patent that shows illuminated buttons appearing on the back of a prosumer DSLR camera (7D/5D-like design), hinting that the feature may be added to the maker's future models. Details are sparse at this time, but an illustration in the patent shows a series of buttons with what appears to be a row of LEDs behind them.
The patent implies that this tech is about lighting up buttons while simultaneously preventing light leaks, explaining that this particular design: "enables a letter or character on the surface of a button to emit light uniformly [...] without providing any dedicated separate member for light guiding and light shielding, and can prevent light leakage to the inside and outside of the device."
As with all patents, we can't say for sure when (or even if) this feature will make its way into a Canon camera, but it seems like a no-brainer and something that would be simple to implement. Check out the full patent for yourself here (Japan Patent Application 2017-147019).