It depends. I read JEPs quite often as part of my job. They are nice as a sum up of the intent behind the feature but they kind of hide the discussion and commits. Also one Java feature may encompass multiple JEPs.
Go‘s github discussions on the other hand, give me live-view of the latest state of the experiment. I find both useful and don‘t prefer either.
That's not the spirit of Go. They will implement their NIH version of JEP/PEP, just one with an awkward interface, held together with duct tape, and missing obvious functionality, then do another round and get 70% of what JEP/PEP do in a second attempt after 10 years.
Go‘s github discussions on the other hand, give me live-view of the latest state of the experiment. I find both useful and don‘t prefer either.