Got to thinking...
Suppose 2D openings show 5S/4-5D and less than high-reverse values, maybe a Rule-of-Twenty 10-count to an ugly 15-count. Responses fairly simple. Maybe 2H natural, NF, constructive. 3C as the ask: 3D minimum (4C re-ask), 3H/3S indicating stiff and max, 3NT no stiff max. Something like that. Maybe sexier, but whatever.
What kind of impact on system?
Well, the early idea was to alleviate the sequence 1S-P-2H-P-3D, a terrible sequence, by making sure Opener has extras for this sequence, and that the sequence is rare.
However, more is possible, very much more.
After a Forcing 1NT, many (like me) tend to have 2+ clubs for 2C, 4+ diamonds for 2D. Add in intermediate jumps (3C/3D/3H as 5-5 intermediates) and a GF 2NT relay, and you have a nice little approach. However, what if 2D openings show 5S/4-5D and light opening strength?
Then, 2D can now, by Opener (1S-P-1NT-P-2D!) be "Opener's BART." Ostensibly, Opener has a weak major two-suiter. 3H shows the 5-5 intermediate. 2H shows both majors, not 5-5, but extras. 2D ostensibly shows the major two-suiter and weak. That helps when Responder has values. The "do I bid 3H or 4H or pass?" becomes "I know what to do." The "do I bid 2NT" becomes "no problem."
So, after 2D, Responder usually picks a major. So far, so good.
But, Opener's 2D might also be a 4D/5S extras hand, with which he corrects 2H (if that is bid) to 2S, sort of like with BART. Now, there are other permutations and options and the like to work out, and I have a few ideas myself already, but this idea is to enable better sequences in a sometimes-tough auction.
How about after a 2/1 2C response, instead? A lot of us now bid 2C with either real clubs or just some gobbled mess wanting to GF. How about BART again, sort of. Opener's 2H rebid could now show 5H, which is nice for the obvious reasons. If Opener bids 2D, waiting, he has some balanced or semi-balanced hand, without six spades or five hearts in that event. If Responder bids hearts, Opener raises with four. Or, Opener has real diamonds (and extras per force), with which he makes some other call later consistent with that holding. This 2D waiting is coming around, but adding to it because of the 2D opening helps, as the "real diamonds" option is more rare and insured by extra strength anyway.
What about DRURY sequences?
Depends on how sick you are. P-P-1S-P-2C (3-card DRURY)-?
2S = minimum
2H = 4-4 minimum
2D = 4S/3H minimum (in case Responder has 5H/3S?)
Or, 2D could be reserved for the really big hands, slammish in context.
The idea is that using 2D openings to show spades and diamonds solves a relatively rare problem immediately (the worst-case high-reverse sequence), but it also frees up a 2D rebid in many sequences to help our side better handle major-suit strain problems, if you add in a strange-sounding concept I call "Opener's BART."