I too am expecting the gun class to be Musketeer. It wouldn't be the first time Yoshida plays tricks to try and get people to brainstorm about his words just for fun. My best bet is that when he said "it's not going to be what people are expecting", he was mostly referring to the playstyle. A lot of people are basically expecting something identical to Archer but with a gun, and I'm sure he'd want something more different. But as for lore, guild and name, yes, my bets are all on Musketeer.

With all that aside, I don't really mind which it will be, long as it will come with one-handed gun/s. I've got enough of two-handed guns in FFXI.