I still think they should tell us.

When Southwest announced that people could start flying with their small pets, the Chief asked how someone would know ahead of time whether any of one's fellow passengers were 4-footed.  The answer boiled down to "you won't."  Not a good answer when you're allergic to cats, dogs or both.  

Finding out only at the gate that you'll be spending however many hours in a tin can with one or more allergens means you can't prepare medically or try to get a different flight.  They're potentially putting people's health at risk.  They need to do better.