This would be a very useful addition to the Arpache SX/5 MIDI VST plugins - to hold down notes/chords played through the arpeggiator until either new notes are played or the function is stopped.
The feature is included in the Retrologue 2 arpeggiator.
I’m currently using version Cubase Pro 8.5 but assuming this feature is still missing as it’s not mentioned in version 9.