So, adding another convention to be learnt just to save 1 letter is arguable.
This is certainly a valid concern, and I would not have done it just for saving one letter. But, as Bob already showed, it can save a lot more in descriptions of multi-leg moves through the bracket notation. There it was a constant annoyance that trajectories involving larger leaps had to be split up in separate orthogonal and a diagonal parts. E.g. the compound of Griffon and Manticore can be written as [K?fsQ], but the compound of Osprey and its pseudo-rotated counterpart A-then-R would have to be written as [D?fsB][A?fsR] this can now become [S?fsQ]. So these new shorthands are mainly intended for use in the bracket notation, I would not recommend writing the Squirrel as NS or the Lion as KNS. The A was already taken, so I could not really find a natural abbreviation for the Alibaba move; not so many letters are left anyway, and it was pure coincidence that there was one that could be associated with a verbal description that at least has some mnemonic value. That this then also worked for the GH compound, in exactly the same way, was in fact an incredible coincidence, which I could not resist. (Although I don't think any piece that is already in use would actually need this.)
This is certainly a valid concern, and I would not have done it just for saving one letter. But, as Bob already showed, it can save a lot more in descriptions of multi-leg moves through the bracket notation. There it was a constant annoyance that trajectories involving larger leaps had to be split up in separate orthogonal and a diagonal parts. E.g. the compound of Griffon and Manticore can be written as [K?fsQ], but the compound of Osprey and its pseudo-rotated counterpart A-then-R would have to be written as [D?fsB][A?fsR] this can now become [S?fsQ]. So these new shorthands are mainly intended for use in the bracket notation, I would not recommend writing the Squirrel as NS or the Lion as KNS. The A was already taken, so I could not really find a natural abbreviation for the Alibaba move; not so many letters are left anyway, and it was pure coincidence that there was one that could be associated with a verbal description that at least has some mnemonic value. That this then also worked for the GH compound, in exactly the same way, was in fact an incredible coincidence, which I could not resist. (Although I don't think any piece that is already in use would actually need this.)