For me, this is much risky for sure especially the last few weeks/months lot of bitcointalk users who able to borrow some Bitcoin or other cryptocurrency were defaulted by the borrower. Especially even how trusted/reputable bitcointalk member you are, there's still a bad side.
Speaking of Blockfi with 8.5% interest per annum, I'd rather go use this than peer-to-peer lending.
But using Blockfi seems lot of requirements needed? like KYC?
Or the difficult part here is the minimum you will lend or deposit to them, it seems like a huge amount.
There is always that risk of losing money when we enter any business.
To address the risk of not getting payment from lending with P2P, the lender has the option to ask for a collateral from all borrowers such as another token that can be sold easily on exchanges. The downside with that approach is the lender will probably have less number of borrowers.
Entrusting your money to a third party for lending is also risky. We all know any centralized platforms are favorite target of hackers. I don't know much about Blockfi. Maybe they have an insurance for their lenders in case something wrong happens but who knows if they can cover all once they get hacked? Not to mention your personal data could also be exposed and sold in the black market.
Between P2P and a centralized lending platform, I think it's still better with P2P if you consider the risks involved.