I've been thinking about this since "The Substitute". Couldn't 108 be the number for Jacob? I know that Jacob seems to be quite ancient, but Wallace as a name has existed for centuries. It could be that it was his surname before he became the protector of the island... and that that's why he has a thing with numbers and the numbers of the last new candidates add up to 108... maybe that's why he asked Jack to dial 108 at the lighthouse, to communicate with him or something... Just a thought.
This, of course, doesn't exclude the possibility of Desmond being one of the remaining 6 candidates, as there's still 1 missing in Ilana's list, and many names that we haven't got to see on the lighthouse dial.