I noticed that after updating Unity the emission channel doesn't produce HDR effects, even if the Emission Power is set to very high values. To fix this I cannibalized the Standard Shader and its implementation of emission channel:
on line 704 of SpriteShaderGUI.cs - replaced this
_materialEditor.TexturePropertyWithHDRColor(_emissionText, _emissionMap, _emissionColor, new ColorPickerHDRConfig(0, 1, 0.01010101f, 3), true);
with this
_materialEditor.TexturePropertyWithHDRColor(_emissionText, _emissionMap, _emissionColor, new ColorPickerHDRConfig(0f, 99f, 1 / 99f, 3f), true);