After extensive consultation with market participants, LCH.Clearnet has decided to move to OIS to ensure the most accurate valuation of its portfolio for risk management purposes. LCH.Clearnet already uses OIS rates to price the rate of return on cash collateral.
LCH.Clearnet adopts OIS discounting for $218 trillion IRS portfolio
LCH.Clearnet re-values $218 trillion swap portfolio using OIS
I guess the argument is since the swaps are collateralized (through variation margin payments), you should use are rate lower than LIBOR for discounting.
I don’t see how they get OIS rates beyond two years for USD given the liquidity of the OIS markets