Obviously its less than this but I calculate that if addresses were distributed as evenly as possible then the current maximum self custody whole coiners is 2,382,481.

This is because there are 996,285 addresses holding one or more bitcoin and together they hold a total of 18,507,569 bitcoin. This leaves 1,386,196 left given the current supply.

So if we say that each address with over one bitcoin is held by a different person and all the other bitcoin is evenly distributed so that each person holds a total across their addresses of one bitcoin then the total is 996,285 + 1,386,196 = 2,382,481.

Obviously wrong but a theoretical maximum.