BIP20 proposes increasing the loan-to-value ratio to 67%, which will unlock more borrower collateral and place additional pressure on the bnUSD peg.
A rebalancing threshold of 10% will give the bnUSD peg more elasticity so it can absorb the demand, and also lessen the impact of reverse rebalancing on borrowers: any ICX added to a borrower’s collateral position will be at least 10% more valuable than the bnUSD debt minted.
As with BIP19, BIP21 is a temporary solution until the rebalancing mechanism has been further refined (discussion here).