Your chat room gonna be success only if you offer something different, unique and special features in your chat room.
Chat rooms are for teenager for the most, few year back I join chat room everyday for flirting some girls. Chat rooms are still very popular in my country.
Have never liked chatrooms, there old school unless its very niche like others have said and unique then it wont take off IMO the net is flooded with chatrooms.
Chat rooms are are best way to waste time. Thats what I did when I wasn't aware of this fact After realizing I left using it....