Yes, Season 6 - there is already something up on Spoiler Fix.
Episodes 6.01: Heartland
A Marine gets in a brawl inside a bar. When the bouncers kick him out, he finds two Marine buddies barely breathing between the trash cans. One doesn't survive and the team is called in to investigate. Gibbs goes back to his home town, where we meet his father. Tony, Abby, Ziva and McGee also appear.
So if the 'also appearing' is correct, it looks as if the team isn't being split up - what has Gibbs done, hired a hit man for Vance *g* - which is good.
OTOH, there is no mention of Ducky appearing in the episode, which isn't so good.
Having said that I:
a) Don't know how accurate Spoiler Fix is. Can anyone help me out here, please?
b) Seem to recall from seeing it a few times over recent weeks *g* that not all the names of the regulars always appear.
Oh, and either Gibbs was lying in The Bone Yard when he said his father was dead, and given he was talking to the Mafia at the time, I suppose that's not beyond the realms of possibility. Or the dear PTB have messed up again with yet another inconsistency. Cynical moi says the latter.
ETA 23rd May: According to information received this morning from Harriet, although Heartland has been shot, it will not actually be the opening episode of Season Six.