If countries offered Government services including education in English, it would hugely assist the movement of people and capital throughout the continent.
Consider: you are from Spain, and have been offered a job at a great company in Germany. You will speak English at the office and probably get around the city speaking English. But: your children need to learn German, fluently and immediately, in order to continue their schooling?
An official EU English would help pave the way for National Governments to offer services in both the local language and English.
If on the other hand you want all services to be available in English everywhere, then I don't think that's a realistic expectation, since it would require all public-facing government employees to speak decent English.
Because you're not only learning the language you study, but also the culture, norms, and values of the people speaking the language. One might be able to translate "Gezellig" (Dutch, cozy) of "Fika" (Swedish, afternoon tea) into English, but context and understanding will be lost in the process unless the English listener knows these distinctive words and their meaning within the cultural context.
Dutch and Swedish are still closely related to English by language as well as culture, imagine languages with no relation to English whatsoever; this "lost-in-translation" effect will be more pronounced.
A future universal translator might be incredibly good at translating, but will never be a substitute for human cultural understanding without having to explain every caveat and cultural intricacies to the user.
By all learning English, we can have a shared language, we're all able to understand each other in real-time, without technology, with less cultural ambiguity when interpreting.
And why wouldn't we learn English? Learning a second language is very achievable when you're taught in school as a child, and Engish seems like a good compromise between Romance languages and Germanic languages since English has a shared vocabulary with both.
Finally, I'm of course biased towards learning English, coming from a country where English is a mandatory subject in school. That being said; I assure you that no matter how good the translator; Seinfeld sucks in German.
Being able to classify europeans in first class (allowed to work), and second class EU citizens (PIGs, yellow jackets,... etc), probably.