I don't think anyone, including the airport, believes that Bristol will become a hub for long haul scheduled travel. They say as much in their master plan that looks forward over the next twenty years where they suggest that only about four scheduled long haul routes, mainly to the USA, might be viable.
Where the 787 will change things at Lulsgate is in its ability to reach non-stop without load penalty charter destinations such as Florida (the 767 just about manages this), Cancun (for which the 767 needs en route refuelling) and resorts further afield.
As for infrastructure changes necessary to accommodate a 787, the airport's £150 million expansion plans have now been passed by the local authority but there is still a question as to whether the sec of state will call the whole thing in for a public enquiry.
The plans include, inter alia, stands for larger aircraft and airbridges to some stands as well as a bigger apron, accomplished by demolishing the old terminal.
The full length parallel taxiway is too narrow for a 787 (wings would overhang the boundary fence) but they anticipate dealing with that by turning circles and backtracking.
No-one that I know thinks the 787 will push BRS into a higher division (in football parlance) but it will enable more flexibility from the airport on long haul, mainly charter routes.