If wanted, I can provide escrow in BTC (but then I also want to lender to put in some BTC of his/her own as an incentive to pay back the collateral)
This makes no sense. The lender already gave you the DRK so no need for further exposure by him, your BTC are safely in escrow --> 0% risk for both parties.
Ok, but after I pay back the DRK, he has no more reason to pay me back my BTC, no?
I am new to borrowing like this, so please correct me if I am wrong.