Well you have to keep in mind that the BWR has the 302% range when COUPLED with the Brompton 2 speed derailleur. The BWR hub itself is just a 3-speed with 50% gear steps (middle is direct drive if i am not mistaken), which as a standalone hub is quite inconvenient. When it comes to 26" wheels you are not limited by the tight clearances of a Brompton rear triangle so you can use pretty much any IGH out there. I suggest look at Shimano Nexus or Alfine. Sturmey Archer is also something worth looking into depending on your project.

Since there is nothing special in the BWR, a hub is a hub, it can be build in any wheel as long you have the correct spoke lengths, rim drillings etc.

-Carcinogent