The TLDR is that I don't see how I'm supposed to believe that this discourages sites from using invasive fingerprinting techniques if those sites are essentially required by holdbacks to still have those invasive fingerprinting techniques at the ready: and 1 in 10 requests even from a browser that implements WEI will still be subjected to those fallback techniques, so your browser/device is still basically guaranteed to be fingerprinted by any site you visit regularly.
You can't discourage the development of something and require it at the same time.
And if the experience of non-participating browsers is so much worse that it's obviously better to implement WEI, then we're right back to the same DRM and competition questions that we had before.
If holdbacks are rare enough that sites can ignore them (or statistically filter them out and determine if a browser actually implements the spec), then those sites don't need to have a fallback mechanism and we're right back to DRM. However, if holdbacks are common enough that sites can't ignore them (and if they can't statistically determine whether or not holdbacks are holdbacks or a non-implementing browser), then everyone is still going to be subjected to the fallback techniques that Google says it's trying to discourage.