They won’t be the first. Original AMC did for years with 206Ls. Back in the days, we had six or seven of them. we flew IFR with it. However, we did do as much as in twins due to fuel load. It just didn’t have enough payload. There is an OpSpecs for an authorization for single engine IFR operations for part 135. I believe it is A047. I think it does say that the ceiling must be enough for an auto. It doesn’t give spec number though.