Above is an industrial version for hvac.
I was reassembling a telephoto camera lens recently and had this in my hand and thought, hmm...
Many are very robust and ideally sized for someone to experiment with on a small simple two stroke. They have little levers on the side that a throttle cable could be easily attached to.
Butterfly plates, round slides, flat slides... round bores, oval bores, etc. Each with it's pros and cons. I'm surprised I can find no reference at all to experimenting with an iris.
It may simply be that it would work just fine, theoretically perhaps even better, but the tiny improvement is offset by the enormous increase in complexity, cost, and reliability. (edited)