I know it’s not very common notation but it’s starting to come into use in some modern scores - is it likely to be able to do this at any point in the future?
Can you provide any examples? I’d be very curious to understand the context, and whether it can still be treated as a functional chord and if you can collapse it to a horizontal mode (though that’s not really my own approach).
I’ve done this as shorthand for something like a Dmaj7 imposed on a C7. Otherwise you have to specify a 9 and a b9.
#11#15 is quite elegant.
Why wouldn’t you simply write
I doubt I have ever played with any musician that would correctly play C7#11#15 without taking a minute or two to figure it out.
I’m not saying Dorico shouldn’t allow it. I don’t see where supporting that would cause any harm.
With the C7#11#15 construction, are you trying to indicate that the D and C# should be a maj7th apart? (Of course, the D isn’t implied in that spelling. We’d need C9#11#15.)
Generally the 9th is implied by the #11th.
i find that writing chords like Dmaj7|C7 often ends up with clunky voicing. #11#15 avoids this.