All these pieces can already be described through the general mechanism XBetza uses for multi-leg moves. The notation you proposed is much less general, and can handle only some very specific cases. E.g. D/W describes a W followed by D as well as a D followed by W move, as well as simple W or D moves. But what if there is a piece that only does simple W, or D after W? In XBetza you can describe each of these moves separately, e.g. mafmpafW would be a move that makes 3 W steps in a linear fashion (f), where the square reached in the first step must be empty (m), while the 2nd square should be empty or hopped over (i.e., its occupant is completely ignored, mp). That is, it is a W followed by D. The bent version would be mampafW, i.e. it would drop the directional f restriction after the first step. Writing an s there would force a 90-degree turn at that point.
It is true this makes the description of your W/D a bit cumbersome (WDafmpafWmpafafW), but that seems justified for a piece that really has a rather elaborate and complex set of moves: three different ranges (WDH), the latter half lame in a multi-path way (can be blocked by two, but not by a single piece). By assigning a very specific (and therefore hardly ever useful) meaning to a certain notation, you can of course always be more compact in the rare case where that notation would be useful.
Note that when the Betza j modifier is interpreted as 'must jump over exactly one piece', the W/D could be written as WDnHjH, which is also not so bad. And at least allows the piece to have an nHjH move without having either W or D.
All these pieces can already be described through the general mechanism XBetza uses for multi-leg moves. The notation you proposed is much less general, and can handle only some very specific cases. E.g. D/W describes a W followed by D as well as a D followed by W move, as well as simple W or D moves. But what if there is a piece that only does simple W, or D after W? In XBetza you can describe each of these moves separately, e.g. mafmpafW would be a move that makes 3 W steps in a linear fashion (f), where the square reached in the first step must be empty (m), while the 2nd square should be empty or hopped over (i.e., its occupant is completely ignored, mp). That is, it is a W followed by D. The bent version would be mampafW, i.e. it would drop the directional f restriction after the first step. Writing an s there would force a 90-degree turn at that point.
It is true this makes the description of your W/D a bit cumbersome (WDafmpafWmpafafW), but that seems justified for a piece that really has a rather elaborate and complex set of moves: three different ranges (WDH), the latter half lame in a multi-path way (can be blocked by two, but not by a single piece). By assigning a very specific (and therefore hardly ever useful) meaning to a certain notation, you can of course always be more compact in the rare case where that notation would be useful.
Note that when the Betza j modifier is interpreted as 'must jump over exactly one piece', the W/D could be written as WDnHjH, which is also not so bad. And at least allows the piece to have an nHjH move without having either W or D.