I believe they’ll have to bite the bullet and go for the outwash front wing. They should be able to beat Ferrari at their own concept with it. Inwash wing and high rake does not seem to be a winning combination.
It took Ferrari a year to optimize this.
It will take RB some time to make this work... as they will need to completely change the concept of the whole car. It's not only the FW they would need to redesign, but also the rest of the car as it interacts with the FW immensely. They would be on a huge learning curve to discover all benefits of this concept...
And then, when they finally mastered the concept a bit, it will be the end of 2020... after which we get completely new regulations!! So they can start from scratch again. Going for a new aero concept is not a realistic option for RB now. They are locked in to what they have.
If they cant make their current Aero concept work, 2020 will be another lost year.