The Audi S1 RX will be very unlikely, EKS racing was until 2016 not supported by Audi so for sure Audi cannot license a car that isn't even completely their own. From 2017 on EKS has Audi factory support I believe.
It will feel weird though, knowing half the top RX cars will not be in the game and that we will play with more unkown cars, no Peugeot 208 RX, no audi S1 RX, no ford fiesta RX, but we have a honda RX coming out of thin air. Luckily we will have the ford focus and volkswagen polol gti. I mean, if they wanted to bring out less known cars, they could have gone for the citroen DS3, the kia rio, or even the mitsubishi mirage, the honda isn't even in the leaderboards.