I suspect its not the porting of it to linux thats the issue, its supporting it. Linux is a moving target, and one that's moving fast.
Which version of the libraries do you link against? will they still be there in the next release? are they the same on debian/fedora/suse? Getting things to work on Linux can be a real headache. If anything needs to be a kernel "module" they you have a real nightmare. The nVidia drivers are a good example of this - upgrade your kernel, reinstall your X drivers.
Unless you want to supply a "sealed box" solution (ie. boot up into RISC OS, if it all goes wrong put this CD in and reinstall) I wouldn't want to support it. Sure, a linux expert could keep it running, but someone who's just downloaded Fedora and installed it - they'd expect support when FC5 came out, as would a debian user, a SUSE user.