As I said, I do think being too strict on it would cause too much queue time. Honestly, I cannot possibly estimate what would lead to acceptable queue times, because I have no data on how many people are looking for a draft at a given time.
Much like normal matchmaking, the pool of players considered would grow larger as the queue time increases, but it should probably start larger than exacts ranks. For instance, it could put bronze + silver together, gold + platinum and diamond + mythic. Or, since I believe the gold population is significantly larger than the rest (I could be wrong), it could be bronze + silver, gold, platinum + diamond + mythic. Or it could be any other split that makes sense to someone who actually has the data.
Again, I cannot possibly know whether or not it's feasible from a queue time perspective, but I thought it would be an interesting discussion w.r.t. whether or not they should consider it in the first place.