My Response Structure to Jacoby 2NT:
For unbalanced hands, Opener can either jump to the four-level, bid Three Spades, or bid Three Clubs.
3S = Minimum, stiff or void somewhere. Responder can next bid 3NT to ask for the stiff. Opener bids a stiff minor. With a stiff in the other major, Opener bids 4H. If spades are trumps, 4S shows a void in hearts. Last train, if available, might be used. Thus, a "minimum" with a club stiff is more flexible than with a stiff in the other major. A diamond stiff is more flexible if spades are trumps.
4-bid = trick source, with a stiff or void in the lower of the two remaining suits. Thus, 4C shows a 5-5 hand, concentration of values in clubs and the major, and a stiff or void in diamonds; 4D shows 5-5, clubs and the major, and a stiff or void in diamonds. 4H, if spades are trumps, shows 5-5 with a stiff or void in clubs.
3C = other shortness. 3D asks. If Opener has a stiff or void, with extra's, he shows the stiff or void. The version I play needs fixed here. I use 3H for the other major, 3S for clubs, and 3NT for diamonds. However, I think this should be 3NT for clubs, 3S for diamonds, and 3H for the other major, because this maximizes the ability for Responder to use 3NT as Serious 3NT when Opener cannot himself distinguish "minimum" from "slightly better than minimum" through 3S and a positive reaction to Last Train.
If Opener has the 5-5 trick source with a stiff or void in the higher suit, he bids 3C and then jumps to the four-level after 3D. So, for example, 1S-P-2NT-P-3C-P-3D-P-4C shows a club-spade two-suiter with shortness in hearts, ...4D a diamond-spade two-suiter with shortness in hearts, and ...4H a heart-spade two-suiter with shortness in diamonds.
With a balanced hand, Opener can bid Three Diamonds, Three Hearts, Three Notrump, or Four-of-the-Major.
Four-of-the-Major is weakest. Three Diamonds shows most non-minimums. 3H shows 5422 and just above a minimum. 3NT shows a sixth trump and just above a minimum. Cuebidding follows all.
The structure helps to gain more definition to each call, but the approach is still quite similar to standard, in a sense. With balanced hands, Opener is making primarily a quantitative bash. With an unbalanced hand, Opener is making a more defined shape bash. With the trick-source hand, Opener is still making a Picture Jump, but with more definition to his call (as to the shortness).
Because of this structure, we have some improvement, but it seems apparent that Responder will want to have a hand that can handle both shape bash and quantitative bash bidding. That analysis will follow next.