An SACD or a DVD-A would be much more expensive to manufacture and it would jack up the price, making it an even more niche product than it already is. And I could be wrong, of course, but I don't think there are many people who like this kind of music and own an SACD or DVD-A player.
Well my first choice would have been a vinyl reissue, but if it must be digital (to accommodate extra tracks for instance), a hi-rez format would be very nice. Tahra is reissuing Furtwangler on sacd for about 10 euros a pop these days.