Maybe this was brought up before, but just in case, I’d talk about my thought on this.
I think it’s pretty fair to say that, when using alternative note heads in a normal staff, let it be cross or square or triangle, things like that, it would likely mean playing the instrument in a different and unconventional way. It probably should trigger an alternative playing technique rather than do nothing.
And for alternative playing technique, maybe it’s better if we can also choose to send certain playing techniques to a different midi channel, so that we would be able to trigger what isn’t covered by the original sample instrument. For example, knocking an instrument, or plucking the piano. Giving that artificial harmonics playback is likely already on the horizon, it might be a good idea to make things more flexible so that there’s no need to get a full version of Kontakt or HALion just to dig into the instrument file and inject some additional samples (which few people would like to do I guess, and it’s not even whether they own Kontakt or HALion or not).
And speaking of instrument knocking sound, it would be great if Dorico can include a sampler/SF2 player so that when there’s a need for unconventional sound there’s no need to get another sampler elsewhere. The sampler/SF2 player should provide a way to turn off key tracking (so that the pitch doesn’t shift when not playing the base note) of course. Sure, such thing would likely produce worse sound than a properly made instrument but it’s still good for emergency use, for example, when writing for a less conventional instrument (or playing technique), just search online for a sample and drop it in and problem temporarily solved.
(Better yet, maybe the sampler should provide multiple sample slots/layers for different techniques so that there’s no need to load multiple samplers to finish the job, but it would probably need a lot more works since that would mean implementing a way to send playing techniques without the use of playback templetes.)