The first thing to do this would be to improve the ranking of a Round Robin in a X-way tie in this way, that the top X players are awarded the 1st rank. This is not the case. Do you see this on Fizzer's immidiate roadmap? ;)
EDIT: You asked why we cant have coin RR tourneys. You did not ask why it is not possible. I believe it is possible. But I think the reason why we can't have it atm is the tie. Thats why it was not implemented. And that is why we cant have it.
Yeah, the logic for resolving multiple players winning from the same price pool is already implemented for team games and tournaments. We could just use that same rounding-down algorithm for just splitting the coins if you end up with a 4 way tie.