It's a minefield, trying to figure out how to name planets. Some will undoubtedly get common names (51PegB was given the unofficial name "Bellerophon", after the Greek hero), but I think the best way to name them is use the convention they use in Star Trek...call a planet, let say Rigel 8 (or VIII) if it's the 8th planet orbiting Rigel. Or, if it's a star without a proper name, say HD7099B etc etc. You can see the problems cropping up here with naming planets.
Probably the best way is to ask the inhabitants of the system what they call it...when we get to meet them
Then we can call 40Eridani A III...Vulcan
