Since the change involved only the interactive usage, and apart from
\# as a symbol in replacement expressions only makes hitherto illegal
input legal, it should have no effect whatsoever on code stability.

I think that the functionality is user-accessible to a degree by now
that it would make sense mentioning it also in the Emacs manual, in
case people agree it is a worthwhile addition.

Personally, I think this functionality is the greatest thing since
sliced bread, but then I am obviously prejudiced.

-- 
David Kastrup, Kriemhildstr. 15, 44793 Bochum