David Alan Black has made a case for Paul as the author of Hebrews. Not too surprising, since he has a penchant for poking at 100 year old consensuses (he thinks the ending of Mark is original). This is a useful service he performs because there is a tendency for scholars to get more and more comfortable with a dominant paradigm and to think it is more certain than it is.
The first time someone suggests something, he or she may be cautious, tentative. I've found this true with my own ideas. But over time, you get comfortable. Your ideas may seem more certain than you thought the first time. Over time, everyone believes in Q just because everyone believes in Q, not because they've done the hard analysis. (P.S. I still accept Q nonetheless.)
I personally am big on scholarly consensus. If the majority of "I'm willing to come to any conclusion" scholars  have more or less come to the same conclusion for over 100 years, you'd better be some crazy kind of genius to argue something different. Most push back on these things is not driven by evidence but by a certain stubborn comfort in traditionalism.
DAB is certainly smart, but probably not some crazy kind of genius. I'll buy his book and no doubt admire it. I'll certainly admire the fact that he will now be mentioned in every commentary on Hebrews for the next thirty/forty years (the last scholar to argue this was a pre-Vatican 2 Roman Catholic in the 40s--and I'm mentioning him 70 years later!). I hope DAB pulls a hefty royalty.
But in the end, he is an illustration of what happens when evidence isn't the real driving force behind your scholarship (dare I suggest that this is what people want to buy, that much of what is being published right now in biblical studies falls into this category, that the best scholarship will continue to appear in dusty monographs that most people will never hear of?).
I don't think Paul wrote Hebrews for a number of reasons: style, differences in theology and use of specific texts, the fact that I date it after the destruction of Jerusalem when Paul had been dead for about a decade, but mostly because I can't see Paul putting himself in the non-apostolic wing of the early church as the author does in 2:2. I have no doubt that DAB has ingenious explanations for these things--they always are. But as I've said before, many confuse being able to come up with a possible explanation, for the most probable one.
 Scholar = knows the evidence to a very high level as well as the history of interpretation on that issue. "I'm willing to come to any conclusion" means the attempt to be objective and to follow the evidence to any likely conclusion, even if inconvenient.