This sounds like a nice extension to Agents.jl like a package extension or a submodule.
It has to be an extension because the assumption that agents are “point particles” is very fundamental to the way we find nearby agents and this unfortunately would be hard to adjust so that agents have extent… To accommodate for agents with extent you would likely need to create a new space type that starts as a duplicate of the current ContinuousSpace and is then adjusted so that nearby_agents works differently and takes into account the fact that agents have size.
Maybe someone has already worked on something like this. Agents with size are not uncommon, e.g., the bacteria model does something like this but hard coding the size instead.