Yes, that exists. COLDCARD Co-Signing (CCC, Mk4 fw 5.4.2+ / Q 1.3.2Q+) is exactly that: the "limit key" is a second seed you generate yourself (Key C) and it lives on your own COLDCARD next to your master seed. No company holds it.
How it works, per their docs:
• Wallet is 2-of-N multisig: your m...