#1. If you broadcast normal stereo at these lower frequencies, radio's won't decode it? I really don't understand then why nobody has ever asked about it!
Yes, with an OIRT Stereo Radio youll get only the mono portion of the signal (of course if you use a SDR that's different and works)
#2. No RDS?
Indeed no RDS. As the 57 kHz Carrier is not locked I don't know if there would be any noticable distortion when decoding... RDS would also be lacking of the Alternative Frequencies in this area. But RDS2 as far as I read would support them... Let's see what future brings
#3. If I add this, can you test it? If you know of an SDR program that supports it I could test it myself as well.
I don't have a polar-capable SDR program ready but a original OIRT transmitter and the corresponding tuner, so I could test it.
As for clipping, I can't tell. Here is the full spec:
https://www.utdallas.edu/~dlm/3350%20co ... !PDF-E.pdf