This paper describes the 10,000 Instruments workshop, a collaborative online event conceived to generate interface ideas and speculate on music technology through openended artefacts and playful design explorations. We first present the activity, setting its research and artistic scope. We then report on a selection of outcomes created by workshop attendees, and examine the critical design statements they convey. The paper concludes with reflections on the make-believe, whimsical and troublemaking approach to instrument design adopted in the workshop. In particular, we consider the ways this activity can support individuals' creativity, unlock shared musical visions and reveal unconventional perspectives on music technology development.