Some time ago I tried to replace the tonemapper with a different one (sadly I don’t remember which one it acutally was 
)
But with this approach you can even decide if you want saturated or washed out emissive colors by changing the saturation value in the material.
Unfortunately you can’t use the tone mapping settings that you could normally use. So you have to adjust the image inside the post process material and build your own system.
If you want to test for yourself this is the material:
CustomEmissivePostProcess.zip (82.4 KB)