Apparently, the last episode will fast forward about 4 years into the future where Enterprise will come home and be decommissioned and the Federation charter signed. Basically, it's the event the whole series leads up to what with all the things that have happened in this season and the last. There is also a holodeck sequence with Troi and Riker, but I think the important thing to note here is that if they play their cards right on this finale, they could, in fact, continue to make Enterprise episodes if they ever decide to bring the show back and have it make sense (since their fast forwarding four years).
EDIT: link
EDIT: link