I think some people are misunderstanding. What @nefarius is saying is that the giffgaff community would remain the same as it is now (being family friendly and safe for all to use) but would have an addition "chatroom" area which would be accessible to only those who are 18 years old or over. To access this area of the community, age would be verified for example by using an electronic identification system (e.g. Yoti).
Some people will love the idea, others might not. Those that love it could use it. Those that don't won't.