I asked a well known portable console modder if he ever considered making a portable Saturn, and I got an answer that it would be very difficult to do, since the components are stacked like in a Gamecube or Dreamcast. Then you get into the issue that you mod chips virtually don't exist anymore, and that even if they did, compatibility with all the different models would be an issue. And you can't just ignore the system, because it has gems like NiGHTS, Shining Force III, Panzer Dragoon Saga, etc. SFIII and PDS both being prohibitively expensive to find, I might add...
Being a portablizer myself, I can reaffirm that it'd be pretty tough to make one, but perhaps not for those reasons. The multiple motherboards can be worked around as seen by the vast number of Gamecube and Dreamcast portables that have already been completed. I mean, it could contribute to the size issues as seen by the single Saturn portable that's been made being a beast, but that could be worked out. The real problem lies in the sole volatility of the Saturn itself. People over at the Benheck forums complain about N64 motherboards frying; you should see the Saturn! So many components, if you just LOOK at it the wrong way it'll fry.
Just out of curiosity, who was it you talked to about making one?
I just sent a random email to Ben Heck while I was out searching for a mod chip one day. He didn't have much to say about it, really.