There are probably enough votes to get the bill passed in the Senate, but there may not be the 60 votes necessary to ensure that it gets voted upon. Exhibiting my actual ignorance of current congressional politics, I don’t know if it needs 60 votes because of a filibuster–the article doesn’t use the f-word, but it is a standard feature of any Senate vote these days.
I’ve never heard any good reason not to give D.C. voters representation. Doing so would be an integral part of pretending that we are a functioning democracy. The only argument against it is that it might be unconstitutional. If that’s the case, you then immediately change the constitution. I hear that the presence of black folk who vote democratic is the real reason for opposition.