As some outside-the-mamedev-mailing-list code contributors have pointed out in the thread, their contributions aren't really big enough to warrant much vote power, and they don't seem to care anyway what license choices are made. A forum vote is pretty laughable too considering most people here have absolutely no say so in anything to do with the source code.
What people are mostly concerned about is firstly universities and museums being able to use the software without crapping in their pants, and hopefully this will somehow get us there, everybody seems to want it, though like I said multiple licenses over files doesn't clear that up for non-programmers, it does the opposite. Another concern is other people profiting off of their work, and if the past is any indication of the future, mamedev is never going to sue anybody. The Raiden Fighters folks just flat out stole and sold mame and nobody did jack, and we're not talking about Shenzhen. So that part won't change afaik, maybe I'm wrong. In many cases I guess now they could do that legally. The last thing I see this impacting is other programs wanting to use mame bits, having the license info more clear on files will definitely benefit them.