Some concepts might include the transfer of technology. Maybe in the fanfiction, Cerberus tries to reverse - engineer Titan technology for their own purposes. Or perhaps the story could focus on a group of characters from Titanfall who find themselves in the middle of the Reaper invasion in Mass Effect. They could use their skills and knowledge to help fight the Reapers, bringing a fresh perspective to the fight. Also, the idea of Titans being used in the battle for the Citadel could be really exciting.
In my opinion, Titanfall 2's story is great. It has a compelling narrative, excellent world-building, and it keeps you on the edge of your seat throughout.
It depends on your playing style. On average, you can expect to finish the Titanfall 2 story in about 7 hours. But if you take your time exploring and soaking in the details, it could be longer.