Playback of a single unslashed grace note, taking half the written duration of the rhythmic note that follows, and stealing time from that following rhythmic note, will be added in a future update.
I’m sure you’re there already… If the following note is dotted, then the appoggiatura should take 2/3 of the value.
Will it be possible to have unslashed groups of grace notes on the beat, rather than before?
I know this won’t cover every situation, but it would give a way of specifying on/before that would be correct for most things.