I first also thought that it would be a good solution. But what could a conversion program do with a GEDCOM 5.5 RIN tag when you want to import your GEDCOM to FTM?

A RIN is a RIN (Record Identification number), nothing else. I believe it would mean that if a record is referenced 100 times in a GEDCOM, the conversion program would have to put 100 copies of the text in that record in the "FTM-enabled" GEDCOM file. Think of later making a change in that text record...

Or is there a way that it would work? I don't know what FTM 2012 does when it encounters 5.5 tags it doesn't support, I've only read what it doesn't do.