I think that it is a great idea to open an "only english chatroom" , but unfotunately, it will be very difficult to maintain it's popularity and etc.....
I agree that using english to chat in BFF is a great way to improve on our typing skills and typing speed. However, I don't think 好友們 can really improve our English unless there's a 好友 with very good English skill to guide and teach us English. (without paying any tutition fees as well...
) In many English forums, people use all kind of slangs to chat with each others. So, I beleive it would be better to open an "only English chatroom" for a specific topic, such as to learn grammar or to write better. Just opening an "only English chatroom" with no particular topic won't help our English in the long run
just my 2 cents