I have been wondering if anyone has ever tried playing invitational free bids in this auction in an XYZ-style structure, something like:
1♦ - (2♣)
==
X = weak (2♦ raise, 2M NFB) or GF with 5-5 majors
2♦ = art GF
2M = 4+ suit, invitational/constructive strength, NF
2N = nat, NF
3♣ = good raise (UCB)
I am not claiming this to be better than a transfer-based scheme, only wondering if this has been tried and, if so, how it compares with the alternatives.