No I'm not on commission from TLSfx, but I felt they are a little too heavy for such close quarter work and the chances are glass, particularly on the landings, is going to get broke or someone is going to get hit by one as it drops down the stairs or rolls into their face if they are close to the floor. It has to be said that the marshal's did an excellent job on Sunday letting those using BFG's know there was a player at floor level and to be careful, but it did give away the players position (and yes on one occasion it was me on the floor). Obviously safety comes first and speaking for myself I was a lot happier being hit by plastic BB's instead of a BFG
Pyro/BFG's work really well here and doing this could possibly be counter productive to how the games play out but you did say you wanted all sorts of suggestions..
Personally I don't think BFG's should be banned completely, just because they are an effective room clearing tool, but what I would say is ban them from being used anywhere near the stairs. Everyone who has used or held one knows how heavy they are and they can do serious damage if lobbed or rolled at pace. If there is any chance a BFG falls down any stairs, it could do serious damage if it were to fall down the middle. And like Trogg said, the player should be dealt with accordingly.