Bitcoin or crypto-backed loans are nothing new. They're offered by both crypto and traditional financial companies. Even in this forum, it's available. A crypto-backed mortgage is just another kind of crypto-backed loan.

But why do you think it's a smart move to use your Bitcoin or crypto as a collateral when the market is down? Although, yeah, it helps you avoid getting liquidated, it also means you're getting a much lower value of what you have. You're risking your Bitcoin to a third-party in exchange for, say, 40% or 50% or 60% of its value. Personally, I don't think it's worth it.