Panasonic has some portable DVD-audio / DVD-video players:
http://www.prodcat.panasonic.com/sho...ategoryid=1933
They're first generation products, so as expected, battery life is pitiful and prices are high. However, they are a proof of concept. I would expect that decoding MPEG2 video and DTS/DD audio would be more challenging than decoding even high-quality SACD. Plus, the LCD screens suck up a ton of battery life, and would not be needed for an SACD portable.
However, I think that in the short term, DVD-Video/DVD-Audio portables are more likely than SACD portables. It's natural to piggyback DVD-Audio functionality on top of DVD-Video functionality, which seems to be pretty hot these days. In the general consumer market, DVD-Video and audio CDs are the focuses. DVD-Audio and SACD are just bonuses for most people, rather than a neccesity, in both the portable and home markets. As time goes on, DVD-Audio will just be another checkbox item for DVD player manufacturers to add to their players. Plus, these DVD portables also play music CDs, which satisfies the vast majority of people. It's really cool and convenient to be able to play movies and music on the same portable.
In short, I believe that DVD-Audio will be more prevalent in the portable space, because it'll be so easy and cheap to add the necessary hardware to the already existing portable DVD video players.