There are a lot of different types of boundary conditions, and some codes take different actions depending on the variable, so it would be difficult to support everything. I have the Maestro front-end reading in the boundary type, but I usually have to override it to periodic to get yt to work.
One option is to provide just the minimum types of boundaries, a zero-gradient/Neumann/outflow, and a reflection (perhaps that does odd-reflection for vectors normal to the interface). This should cover most of the standard use cases (maybe a survey of what types of boundaries people use would help?). To close the remaining gap, there could be a standard function interface that a user or frontend writer could provide to handle "custom" BCs.
It would also be useful to know what routines need boundary conditions and how many ghost cells are needed.