Proposal/question about patching gr_file_{source, sink} to support a change filename callback

Looking at the gr_file_source code, it doesn’t appear that there is a
callback to close the current file and open a new one instead. I have an
application where I’d like to be able to do that. If it’s not
implemented in some other way I haven’t found, I’d like to implement
this and have done so successfully in other modules for private use, but
my question main is, if I’m not mistaken in thinking this needs to be
done in the first place, is there any interest in me submitting a patch
and are there any side effects I’m not thinking of in adding/exposing
these callback methods in a core block even though the io signatures
will be the same?