What are the limitations involved in moving the location of a toilet when you have a slab foundation?

There are really only a couple of considerations besides time and money. You want to avoid any sharp angles where the new drain connects to the old, and you want to make sure there is sufficient fall over the length of the new drain. A quarter inch per foot of length is probably the minimum fall you can get by with, so over a 6 foot run the pipe will need to drop at least an inch and a half before joining with the existing drain pipe; the more the better.