Happy to report that many Android devices have WebGL active by default now! I don't know the full list, but I know it includes the Nexus 4, 5, and both 7s. The latest Samsung and Motorola devices have it as well. Basically anything with the ARB_Robustness extension will have WebGL activated with no action on the part of the user. I wish this was 100% of devices, but at the very least most new devices seem to have it.