[the Obscure]

Besides the fact that it would make English easier to teach if everyone spoke it the same, I don't see any other reasons that would make a Universal English worthwhile. There are too many countries and cultures involved that use English as a national and/or official language. One of the most interesting aspects of languages is their ability to adapt and morph- such as the way that different generations use slang, and the ways that different Englishes use slang.
I don't think it's necessary or even desirable to teach an in-depth cultural lesson with language, but there are lots of little ways that culture influences language that should be taken into account. For example, in English, using you to refer to someone (Would you like some coffee?) is totally fine but referring to someone by name if they're in the room (Saying "Would Amy like some coffee?" to Amy) would be considered pretty condescending. But, if you're speaking in Japanese, using 'anata' would be pretty impolite, so it's best to either use the person's name, or omit the subject altogether. I takes awhile to get used to people talking to you as if they're talking about you when you're not used to it, but it's ridiculous for me to expect Japanese people to speak to me in Japanese as I would speak to people in English. Just as Japanese language is a reflection of Japanese culture, Canadian English is a reflection of Canadian culture. That's what makes it exciting to learn languages. If we tried to make Australian, American, British, South African, Indian, Philippino English, etc., etc. the same, then the English language would be dead.