um... no one?
I hope the Typhon Pact won't fall so soon. There's much potential (in-universe and storytelling-wise) in the Pact, it would be a shame. Think of what could still happen! New powers joining, internal fracture, transformation into a new state or Federation... They haven't even met the Taurus Pact yet!
Well, counting a trilogy as an arc is... obvious? Imho, it was just a 'trilogy arc', in contrast to TP which is ongoing with no end in sight. As is Project Full Circle (real world perspective - no new book before 2014
Another ongoing arc is the Andorian struggle, started with DS9-R and far from a conclusion.
An ongoing TNG storyline is the character development, slowly preparing us for the crew of 2387, whether it meshes with the comic (Data's return, Lt. Aneta Šmrhová, Joanna Faur, retiring Picard) or not (Data's return: how).