An opposition won't be necessary. The application will 99% get rejected, since the term "bitcoin" will be deemed descriptive or even generic. On the small chance it slips by the examiners, then an opposition would be in order.
Not sure I agree with this. If you're saying that the word is too common to trademark. There's always the first person to file the trademark for a term. And they're the ones who get it. And Bitcoin wasn't even a word 3 years ago. Let alone trusting the evaluators to be familiar with it even today ... It will be rejected if someone else has trademarked it but not sure it would for any other reason?