There is a method:
Filename class>>pathForRemoteHost: aHostName
"Convert the host name to a path name prefix used for accessing
files on the remote host."
self == self concreteClass
ifTrue: [^self error: (#ThisPlatformDoesNotSupportFileNameSyntax << #dialogs >> 'This platform does not support a file name syntax for accessing remote files.')].
^self concreteClass pathForRemoteHost: aHostName
However, the method pathForRemoteHost: is nowhere reimplemented (at least in 7.4). In other words, this method always produces an error. Does it not deal with UNC file names for example? It creates odd behaviour in the sense that you can take a valid filename (on a network drive), convert it to FileURL, but cannot revert it to filename.