You dont even need fixed point for this. Just never store vertices in world space.
Fixed-point is more natural for certain situations, like representing the position of an object in a huge world
Keep your models each in their own coordinate system near 0,0,0.
No, that will not solve the issue. The reason why using floating point is "wrong" and fixed point is "correct" is not that vertices within a model are in world space, but that entire objects are (necessarily) in world space. Though floating point will still "work" in many situations.
An object (person, car, box, whatever) near the origin might have a position accurate to 5 nanometers, which seems "cool" but is not really necessary -- nobody can tell. On the other hand, an object on the far end of the world might only have a position accurate to 15 meters.
Bang. It is now entirely impossible for a person to walk, as you can only move in steps of 15 meters, or not at all (and people just don't leap 15 meters). It is also impossible to distinguish 10 people standing in a group, since they all have the exact same position. It is further impossible to properly distinguish between objects moving at different speeds. A bicycle moving at 25km/h stands still. A car moving at 53.9 km/h stands still, but a car moving at 54km/h moves at 54km/h.
This is inherent to how floating point math works (it is a "feature", not so much a "bug"). Fixed point does not have that feature. A person can walk the same speed and be positioned the same at the origin or at the far end of the world.
It doesn't matter that the vertices you render are in their own coordinate system if the entire object cannot be simulated properly or if the entire object is culled away.