I don't think this these combinations would occur often enough to justify this. For K and Q the argument is that these are orthodox pieces, which tend to occur in almost any chess variant. It seems better to reserve the unused capitals for something that really could not be done in any other way. Possibly with the exception of P for abbreviating Pawn moves, as the Pawn is also an orthodox and extremely common piece, with an otherwise extremely cumbersome notation. If Pn is taken to mean fmWfceFifmnWn it would save a lot of trouble.
I don't think this these combinations would occur often enough to justify this. For K and Q the argument is that these are orthodox pieces, which tend to occur in almost any chess variant. It seems better to reserve the unused capitals for something that really could not be done in any other way. Possibly with the exception of P for abbreviating Pawn moves, as the Pawn is also an orthodox and extremely common piece, with an otherwise extremely cumbersome notation. If Pn is taken to mean fmWfceFifmnWn it would save a lot of trouble.