I don't see what single-server/cross-server has to do with LFD. Either the LFD system can get you into a Flashpoint group with others from our SWTOR community, or not. That's its job #1, its raison d'Ítre, the measuring stick that determines if it's a success or a failure. The KISS principle in action..
I think this particular aspect is merely a matter of choice, not functionality. As someone pointed out earlier, and also what I experienced in WoW - In a multi-server grouping experience you rarely group with the same players. In a single server environment, you'll see more same players and more of a community-based atmosphere is presented.
Still, it makes little to no difference to me. Both ways have pros and cons. But I would like to see something implemented though. Flashpoints have great storylines. The look like fun. The loots would be nice. But I don't have a spare hours to camp fleet and put a group together. I would rather spend that time playing. As it stands, I have only done about 4 complete Flashpoints. It almost seems like a waste of content. Or at best a carrot on a stick.