I do think Edelman is probably the closest thing we have to a good comp, and that's why expectations really need to be tempered. Edelman wasn't much of an NFL WR until his 5th year in the league, I assume in large part because he had to learn the position much like Gunner now has to.
That said, I like him as a PR and think his skillset can slide well into numerous other ST roles. Which is enough to keep him on the team while he develops as a player. But yeah, I think it'll be a couple years before the full value of having him around can be realized. He has the requisite athleticism to be a real, impactful NFL receiver, something that Braxton Berrios and Riley McCaron lacked. It remains to be seen whether he'll capitalize on that to anywhere near the degree that Edelman has, but at least the opportunity is there. I do think returning punts is a fairly good barometer for the toughness required to play slot receiver, and Gunner has shown he has it by taking the 10 yard returns that come with big hits at the end.