Great idea, but I agree with @fubuloubu that we should plug into Tornado’s V3 plumbing instead of creating our own.
From the PoV of yEarn, this is UI thing: add a toggle in the deposit interface which when switched, the yEarn shares (which are ERC20 themselves) are automatically deposited to the Tornado contracts and the depositor is handed a note, with a clear warning “keep this note safe”. Upon withdrawal, a similar UI element that allows a user to withdraw by supplying an address and the note.
So there is no need for a connector contract even, it’s all client-side JavaScript (Tornado will probably release an SDK with V3).
This is in fact something all DeFi frontends should do, I have previously suggested to Compound to do the same in their frontend which will turn Compound into a giant mixer. Even though Tornado has cDai in their frontend, the liquidity is so low … which implies this is fundamentally a UI/UX issue, Tornado already created the plumbing.