I love the guy long term but here is what I see as pro/con for early production.Everett could be very good and possibly sooner than I think
Con: TE's slow to develop in NFL, he is a raw route runner, big step up in competition, shaky QB play.
Pro: he's a hybrid who based on stuff I've been reading will play WR more early in his career than TE which could remove some of the general slow TE development(and remove your Higbee concerns). Reed and Hernandez, who were used more as WR's than traditional TE's, both got off to strong starts as rookies but injuries hampered both otherwise you might have seen both of them post top 5 all time rookie TE seasons, in fact I'd say likely.
In same offense rookie year Reed only played 9 games as a rookie and his QB was rookie RG3. Reed missed almost of all training camp that year with a knee injury which I remember well because at the time I thought a rookie TE who missed almost all of camp was worthless the upcoming season. In those 9 games he averaged about 15 fantasy PPG in TE premium leagues, which usually will you hovering as a top 5 TE. His pro rated numbers would have hid him at 80/887/5. We don't know if he's as good as Hernandez or Reed of course, just citing similar type players, one used in same system, who got off to strong starts as rookies.
Lack of comp for targets, it's wide open. His YAC ability for his position is elite, this will work a lot better in TE premium leagues but as they bring him along I can see a ton of short passes/screens in his immediate future. Bad OL and they need to give Goff some easy throws to move the chains and this could be nice formula for a lot of short easier completions.