Given the ubiquity of the Walkman and the boombox, I'd say it's highly unlikely that we'll ever stop getting disks that are playable in a two-channel system.
You may have misunderstood your dealer friend, however. The second layer on a hybrid SACD is CD, not 2-channel SACD. As for DVD-A, there was something recently about hybrids that would play on CD machines, but I'm not sure there are any on the market yet.
The more challenging question is whether record companies will take as much care mastering a 2-channel version anymore. It's also possible that the two-channel option of the future won't be a separately mastered layer at all, but an on-the-fly mixdown of the multichannel version.
You may have misunderstood your dealer friend, however. The second layer on a hybrid SACD is CD, not 2-channel SACD. As for DVD-A, there was something recently about hybrids that would play on CD machines, but I'm not sure there are any on the market yet.
The more challenging question is whether record companies will take as much care mastering a 2-channel version anymore. It's also possible that the two-channel option of the future won't be a separately mastered layer at all, but an on-the-fly mixdown of the multichannel version.