It would be possible to rewrite an SNES game for Saturn. It wouldn't really be the same as a Genny->SCD conversion though, since a lot of the work of rewriting those goes away due to the fact that the Genny hardware is actually available on SCD. It would be a lot of work, but not impossible for dedicated people I think. Maybe some tools could be written to accelerate the process, though a blanket SNES -> Saturn translator probably isn't feasible.
As you might or might not know, i'm the coder of Stardust, the SNES emulator for Saturn.
Rewriting a game from scratch is very complicated. There is no direct conversion of graphics, the processor is totally diferent from any format the ones the Saturn uses, so everything must be ripped and turned into the Saturn equiivelent. And of course, if you want any correct gaming representation, you have to read all the source code, understand what it means, and then write equivalent routines in C or ASM. This is a hard task, feasible for simple games, but just plain _hard_ for stuff like RPG's and the likes...
Using a 65c816 CPU emulator could solve some of that stuff, but untill I finish the one i'm doing, there are no 65c816 CPU emulatiors running on the Saturn