It'd be great to have a constant lurking danger always there. The immersion in Cyrodiil is amazing in my opinion and a lot of it is to do with the Imperial City. Whenever I'm travelling from keep to keep and I get a view of the anchor over the White Gold Tower I just get an overwhelming feeling of hugeness.
The same thing happened in Skyrim. Seeing a dragon flying in the distance, not attacking you, but just far away and doing its own thing, created huge immersion.
Having something similar in some areas like the view of a titan flying overhead or hearing a roar in the distance would definitely do the same.
Then every now and then a huge boss fight might occur when the titan lands to fight. You'd get a notification on the screen if you're in the region, like you would if someone takes a scroll in your campaign. There would be a unique image on your map showing its location. It will also have the chance to drop extremely rare and unique gear. This way you're guaranteed that everyone knows its up and will come because of the chance of amazing.
Maybe have 4 titans that are molag bal lieutenants that fly around tamerial and land any where even cyrodiil. It would take at least 25 players to send him/her back to oblivion. Only stays on ground for an hour in area it landed. When the lieutenants dies has cd of 3 hrs but only res by a player summoning there pet/deadra, happens to random player. A portal opens and you see big hands coming out. You have about 10 secs to run or whoever is around. A summoning that went bad. That would be cool somebody summon their pet in trails on a boss. Players run and the Titan kills the trail boss.
That give me another idea summoners that have a 1% chance to summon a Titan. Cannot be controlled and is acted as a bad summon. This could be become beneficial or a wipe. The Titan would attack everything in range to as like Npc/players/adds/bosses.
Dragons would fit in just as well as titans. Either or both. In fact, seeing more dynamic solo/group content would be awesome. Tamriel, as it is now, seems rather rigid
Elder Scrolls lore has them slowly being picked off over Millenia, and by this point in time there are relatively few alive. Daedric Titans may be problematic, but Dragons are outright impossible.
People believe what they either want to be true or what they are afraid is true! Wizard's first rule
Passion rules reason Wizard's third rule
Mind what people Do, not what they say, for actions betray a lie. Wizard's fifth rule
Willfully turning aside from the truth is treason to one's self Wizard's tenth rule