One advantage I've noticed at least (having been a contributor to the Julia language itself), is that it at least makes contributing to the language very approachable. Granted you see lower quality proposals from time to time, but in general, I even question whether I myself would have gotten involved or been brave enough to propose language features if I would have had to do such a rigorous, formal PEP writeup. In some respects, you're restricting the pool of people who actually contribute ideas to the language.
I also have appreciated the "meritocratic" approach of Julia language features; if someone can show that an idea/approach/algorithm is fundamentally faster, more flexible, etc. it's generally been accepted, regardless if the proposer is a first-time contributor or not. That also makes contributing feel approachable and very fair, as opposed to just trying to please a single core developer or playing some politics game.
I also have appreciated the "meritocratic" approach of Julia language features; if someone can show that an idea/approach/algorithm is fundamentally faster, more flexible, etc. it's generally been accepted, regardless if the proposer is a first-time contributor or not. That also makes contributing feel approachable and very fair, as opposed to just trying to please a single core developer or playing some politics game.