After some deliberation, the people on the Allegro 5 discussion list have decided that Allegro 5 is not worth pursuing. Hence, it has been scrapped. Not that it really took off anyway, so nothing much was lost.
However, there has been some discussion about Allegro 4 on the developers list, too. Unfortunately, it looks like 4.0.3 will be the final release ever. Sad, but true.
Note that there are plenty of alternatives around, and the source code is available so anyone who feels up to it can take over maintenance, if they so wish.
So long Allegators. See you over at www.libsdl.org.