According to the 2.2 Migration Guide, File class is deprecated, and RhoFile should be used instead.

However, RhoFile does not support reading/writing binary files. Actually removing File, then, would lose functionality. There are many other methods, as well, that are present in File that are not in RhoFile.

File is documented as being a subset of standard Ruby File. A pretty complete one, by my estimation.

Is there anything to be gained by replacing existing code that uses the File class with RhoFile? Is there any possibility that File will actually be removed in the future?

Is this mainly to support Javascript coding?

If File is not being removed in the future, the documentation should be updated to reflect that. There should be some clarification as to when you would use RhoFile instead, and why.