Ironically , I was just looking at this same "build" last week. ( I am planning a few porch swings around our fire pit also)
The one "Drawback" I see with permanently mounted swings (or fixed benches for that matter) is that the users can not adjust their distance to the fire.
Everyone likes to sit a different distance from the heat (and smoke.)
The fire size and intensity is always changing. And the outside temperature varies from night to night too.
I have come up with a plan/idea that should enable me to end up with an adjustable porch swing.
If I ever get around to actually getting it built I will drop back and post a few pics.
"Someday".
Until then we just use lawn chairs.