This is (much less of a) problem on a flat layout, like what used to be called a "desktop" case, instead of the conventional tower. Then the weight of the card is just pushing straight down in the direction the card already wants to be oriented.
I'm using a pretty heavy modern GPU (ASRock OC Formula 6900XT) in a Cooler Master HAF XB with that layout, and sagging and torquing is not much of a concern. The worst part is just fitting it in, since there's like 2mm between the front plate and the board-- you have to remove the fans so you can angle the card enough to fit.
I also suspect that if we went to the 80's style "a full length card is XXX millimetres long, and we'll provide little rails at the far end of the case to capture the far end of a card that length" design, it would help too, but that would be hard to ensure with today's exotic heatsink designs and power plug clearances.
I'm using a pretty heavy modern GPU (ASRock OC Formula 6900XT) in a Cooler Master HAF XB with that layout, and sagging and torquing is not much of a concern. The worst part is just fitting it in, since there's like 2mm between the front plate and the board-- you have to remove the fans so you can angle the card enough to fit.
I also suspect that if we went to the 80's style "a full length card is XXX millimetres long, and we'll provide little rails at the far end of the case to capture the far end of a card that length" design, it would help too, but that would be hard to ensure with today's exotic heatsink designs and power plug clearances.