We made sure to at least provide a Windows build of our game for this reason.
We also accidentally used some graphical features which won't work on webgl, so some of our shaders are broken :/
Shader compilation times in html5 are also abysmal, but this is more of an issue with webgl itself rather than Godot.
If anyone has any links to related GitHub issues or proposals, please share them here so we can 👍 them! e.g: godot-proposals#6909