The natural way to do that would be to enclose the part of the description that can be repeated in parentheses (possibly followed by a number to specify a maximum number of repeats). For the Slip-Bishop that would give (afmpaf)F. This notation could also handle pieces like Mao-riders. Or circular / zig-zag riders. So it is a potentially very powerful device. But it is rather cryptic.
Ultimately, we will probably want something like this, but I don't think we need it yet and I'm not currently available to work on implementing something this complex. (Or even dedicating enough time to thinking about how it should go.) So I'd table this for now.
q in the sense of circular doesn't seem meaningfull on slider atoms. So qB, qR and qQ could be Slip-Bishop, Slip-Rook and Slip-Queen.
Ultimately, we will probably want something like this, but I don't think we need it yet and I'm not currently available to work on implementing something this complex. (Or even dedicating enough time to thinking about how it should go.) So I'd table this for now.
This proposal seems perfectly reasonable to me.