Making a pixel-perfect port seems pretty daunting since there's a whole lot of content there, but with a corner cut here and there I can say with absolute certainty that Fallout 1 would work on the DS.  That's not a project for one person though, or even for a small team.  It kills me to say it, but I don't think the homebrew scene has the resources to put a project like that together.  Still, it would be basically one of the greatest things ever if it happened.  Especially if it were open-source with a scenario editor.  Oh man, just imagine it... okay, I'll stop myself before I get too carried away.