At the end of ep. 14, season 2, the laughing coffin member who went by Death Gun had a message for Kirito. He said "Show time" which indicates some action is going to take place.
My 1st theory: Members of Laughing Coffin enjoyed killing other PCs in season 1. When the game ended they were turned to reality where they couldn't murder anymore. I'm willing to bet that at least 1 member of the LC guild was still hidden in the guild that Kirito and Asuna were members of (remember the leak of information going out when the guild went to try to punish/imprison the LC guild?) Some members of the LC guild couldn't give up their old ways, hence some couldn't resist, hence season 2 and the murder of players in GGO. We know there were at least 1 active accomplice (but now I'm thinking more who were in the know) of the Laughing Coffin guild (or more specifically Death Gun) murdering people and Death Gun's brother.
Given that several LC members were returned to reality, it would make sense that they would get into other VR/MMORPG games & play.
What if they stayed in touch? What if some of them still wanted to murder but were frustrated about their inability to do so?
Now, if Death Gun was in touch (we know he was with at least 1 person) with his old guild, and this doesn't mean that all LC members would do this but they do represent the "sick" % of sociopaths in our society, and some of those other members were already in ALO? Wouldn't the members in ALO during the BOB in season 2 do their homework before or during the BOB tournament and have tried to located some of their former enemies in SAO? Kirito would definitely be one of them, he killed several LC members and brought an end to "their" game- SAO.
No imagine some LC members in ALO. You have Kirito, what happened, the fall out and all of the info posted about what happened to the end of SAO. Now add that you've been playing in ALO for a while. Story arc for ALO. Wham! You've ID'd Kirito who didn't change his name and looks and acts like the Kirito of SAO. You've ID'd one of your guild's enemies.
Now you've got the word within the LC guild that THE Kirito is in GGO & is fighting a LC member, Death Gun (Death Gun did ask Kirito "are you THE Kirito?" several times during their first meet up). You watch the BOB tournament, etc. & see that Kirito defeats Death Gun then learn on the news that 2 members of your guild & one of his brothers has been arrested for "carrying out the cause" (AKA murdering PCs). Do you want payback? For some, definitely. Not all but for some payback is desired.
Now members of the LC put another plan in motion (during the ALO story and the beginning of the BOB tournament) & deliver word to Death Gun & his other companions. Kirito and the "old crew" of his in SAO like to hang out in ALO. What can you do? Set up a new plan for payback. Payback for ending their "fun" in SAO. Sure.
So, when arrested, Death Gun, knowing he can't do a thing but knowing other LC members in the loop, gives his "message" to Kirito indicating there will be a reckoning.
Return to ALO.
Kirito & crew (plus the new member Sinon) get this information leaked about Excalibur. Everyone who knows Kirito knows he's into the best and bad ass swords. How to lure him in, "offer" the best of the best swords in theory out there. What's in it for the LC coffin? 1. Payback on Kirito & company. 2. Continue the mission except carry it out in the world of ALO where he & SAO members are believed/known to hang out at. How do they do this?
Theory 2- Another member of the LC coffin has taken over the role of the King of the 4 armed demons (if their stats transfer as Kirito's & company did they're way above average, we know they're lethal and GOOD at combat) and are attempting to so a Bat Man "Dr. Freeze" plan & start messing with ALO big time. Take out the Jotun land (ultimate goal is to rise above the Tree of Life and do the same to ALO) and when things get tough, invite other, unsuspecting PCs to join in the slaughter of the NPCs & animals (servants) of the Jotun. During this, use THE Excalibur (knowing it won't really be given) as "bait" for Kirito (assuming it's not a fake). This has set up the fall of Jotunheim (?) and the eventual fall of ALO (a known favorite hang out for former SAO members & Kirito & company). Give word to Death Gun. Plan is set in motion.
Arrested, Death Gun delivers his ominous message to Kirito. His guild is at work. Send most of the 4 armed demons out into the land of the Jotuns and make it appear that the demon/Excalibur occupied fortress is empty. Fill the fortress with LC members waiting for Kirito to come for the sword.
This theory is a stretch. It's based on the leader of the Jotuns & the Demons.
Ep. 15 gives us clues, word is spread about "Excalibur" or some great sword above Jotun-land. A "quest" is created to get rid of the monsters & Jotuns of Jotun land. We meet the Queen of the Lake, she's a possible AI but she's "different", perhaps the situation changed her to "change". If she has changed then what about the King of the Demons & Excalibur? This is where I got the idea of the Demon King (or the one controlling him) being a member of the LC guild and info from Ep. 14 where Death Gun gives his fateful message, knowing it will be delivered to Kirito.
I think that the 2nd arc of Season 2 is about the LC guild getting cold revenge on Kirito, ESPECIALLY after the GGO/BOB tournament. Like I said, brainstorming from Eps. 14 & 15.
I'm here to watch ANIME!!! Watch Log Horizon!