Desmond is 108 by DHCF

To me, it is apparent that candidate number 108 is Desmond.

To rule out a previously stated theory, Jacob told Hurley "someone was coming" I think that means we can rule out that he is referring to himself as that just plain wouldnt make too much sense.

Next, out of all the people off island, Desmond is the one who has potential to make the biggest contribution. "The rules don't apply to him" and he has always been a pretty major character. There are 3 big hints though that I think make it pretty clear.

1. The name on the dial said Wallace which could be alluding to the Scottish hero William Wallace, Desmond happens to be the Scottish hero on LOST.

2. Desmond spent 2 years on the island pushing the button every 108 minutes, so the number already has significance to him.

3. This is the clincher for me, the episode is titled the lighthouse, Jacob said the lighthouse would help bring someone to the island, so clearly the lighthouse is important (duh!) To look at it simply, what is a lighthouse's function? To safely guide ships and boats to shore. What does Desmond travel around in? A sailboat.

Jacob said now that "they will just have to find another way" I feel like this was a way to stall before bringing Desmond back in while still hinting at his return.