This rule always applied and never was changed. The primary reason was to prevent people from downloading songs to practice on their own, giving them an unfair advantage over other people who can only play the song through the FFR game. The other aspect is originality/exclusivity for the site - strategically, this helps maintain traffic for FFR and keep people coming back to that site. It's nice to have people play the FFR game for songs/files not offered elsewhere. Songs on the DF engine would not be liable under the former, because you can't download DF files onto your SM and practice upon it. But we still want to not duplicate files onto other sites.
The rule when it was first made never predicted that other sites would obtain the FFR engine with people adding their own songs to it. It was mostly towards people who uploaded FFR files onto simfile databases at sites like FFR or bemanistyle. Because of this new situation, I just decided to let it slide since this particular case never was addressed. I'd say that we want original files only starting the next batch. Don't make public releases of files you hold dear to.
I still don't think that DF should be used as a site to "catapult" your files onto FFR. What most people do however is to provide the file to a few other people in private and have them test it. That's probably the best way to get some assurance and feedback.
@mario: there were several other people who submitted DF files, not just you (e.g. beautiful arrhythmia, passage D, etc.)
@Kayla: I guess it's ok if you remove accepted FFR files on the DF engine later on. Now if this was the Tass era, I think the damage has already been done by making any submitted songs public. I think this can be a solution for people who submitted a lot of things on DF namely for feedback. In the future though, it's preferable if file testing is done by private means. When submitting something that's potentially for the domain of FFR, you have to maintain a degree of confidentiality.