Is doing business with Inter.link really structurally different from getting connectivity to an exchange like DE-CIX and doing business there? I know that in theory, you get settlement-free peering at exchanges, but only for those networks that participate.

And who funds Inter.link? Their publicly available balance sheet shows significant, growing debts to a linked company, but it doesn't mention its name.

Depends what exactly you're buying from them L2 yes. L3 no