DavidKok, on 2025-August-24, 10:02, said:
XYNT already has the ability to stop in 2♦ on 1m-1X; 1NT by using the 2♣ puppet and passing. The main advantage I see of using 2♦ as weak natural NF is that opener might pull to the Moysian if the number of cards is disappointing, but this would imply that opener knows the degree of fit better than responder. In practice I think there's no gain here.
If responder is a passed hand, then we play that after 1x 1M 1N, 2D is natural, weak, but promises 5M. This allows opener to bid 2M with 3 and pass otherwise. Responder can remove that option by bidding 2C over 1N, puppeting to 2D.