Consider the floating leg of a IRS on the RFR which is effective today at $t_1$ and has a payment at $t_1 + 3M$.
My question is, when the payment occurs at $t_1 + 3M$, is this the $3M$ forward rate observed at time $t_1$ (forward-looking), or is it the daily-compounded RFR rates observed throughout the $3M$period (backward-looking).
If the answer is the latter, then isn't that what we do for OIS swaps? Meaning all IRS are now OIS?
If the answer is the former, isn't there a lot of uncertainty about the $3M$ forward RFR rate?