What if there were certain Titans that were largely docile. A giant turtle or some such, it might hurt things it steps on but it isn’t chasing or trying to hurt you. But the back of the turtle could provide a location to build your fort.
While a turtle is an obvious analogy, because you can imagine a tower rising from its backs you could also apply this to Titans that would walk upright (think a backpack being built on the Titan.)
If someone kills the titan, perhaps these docile ones would turn to stone and leave behind their body and the structures built upon them.
I also like this idea but I´m not sure if it is worth the effort. I mean the devs would have to add collision detection (what happens when I build a tower on the titan and it walks through a tunnel?), a separate block grid (atm a block is either on 0,0,0 or 0,0,1 but when the creature is moving the block would have to move from 0,0,0 to 0,0,1 in a fluent motion), What about beaconing builds on titans?(would the titan become immortal or would we have dozens of beaconed titan corpses laying around?) What if I build in a way that would restrict the movement of the titan? (i.e. building around the legs)
I imagine the Titans will be able to destroy blocks. The structures on the back would either break, or they would break things they collide with. (It might require a “density” rating for blocks. So when two blocks collide the “tougher” block survives.)
Block Grid
I have no idea how the blocks moving would work. Perhaps when attached to the titan they cease being blocks and instead become part of the entity? (So you’re actively changing the structure of the titan, not the block grid? And when you damage a titan in an area chunks fall off of different block types?)
Beacons
Are creatures immune from harm while in a beacon? I’m not sure.
If the blocks become part of the Titan, and are removed from the block grid, then it’d be possible for the game to say “This isn’t a beacon, yet…” But when the Titan dies it could become a beacon?
Can Titans enter beacons? Because I think some of your questions (i.e. building around the Titan to trap it) is a question that applies to the game currently as well.
I love the devs cute way of saying “hold your horese with your idea, because this is very likely what we are planning to do but dont want everyone to know yet”