Prior to 10.1’s release, Graham was quoted as saying the banner requirement would be dropped in the eventual open source release.
RB 11.1 still says:
It is traditional that the banner must appear eventually (and one of the few requirements of the Inform licence is that the author acknowledge Inform somewhere, for which the banner is sufficient)
but I think that’s an oversight. I filed a documentation bug last month soliciting clarification (I7-2249).
I wrote a Custom Banner and Version extension to facilitate modifying them, but it’s for 9.3/6M62; I haven’t yet updated it for v10.