MP
I should be interested to read views on what options are available to South, responder, on his second turn, ranked by preference. Assuming that you agree with the auction up to that point, of course.
I reckon that there may be up to 3 possible approaches to answering this.
One is to ask: what would GIB bid, sitting South?
Another is to ask: Playing in a GIB tournament, which bid is likely to have most success?
A third is to ask: If you were playing with a human partner of choice, but forced to play something akin to Gibberish, at least up to that point, what would be your preference?
Finally, I have observed that lately GIB is not averse to rebidding 1NT with a singleton in responder's suit. So not averse, in fact, that it has been known to rebid 1N with 5521 shape (there is a thread somewhere in these columns with that example). That being the case, why would GIB not rebid 1N on this North hand? It would certainly take South's problems away.