Hello Patrick
Regarding ETC., could beginners use FM in a specific portion of the passband near perigee?
Power and bandwidth issues aside, technically there is no reason why FM would not work through the transponder, although the equalizing effects of STELLA in the SDX may distort the signal somewhat because it's designed to deal with SSB/CW signals.
Regarding perigee: firstly, of course at perigee the footprint is a lot smaller, so coverage would be a lot smaller. Plus, the spacecraft will be off-pointing at perigee.
I realize it is not as power efficient as SSB and CW
It is also much less frequency efficient - currently, we are designing for a 100kHz passband. An FM signal might take 15kHz of that whereas an SSB signal would only be 3kHz.
The inefficiency from the power aspect that you mention could be mitigated by converting the FM uplink into an SSB downlink, although of course this rather cancels your suggestion that FM might encourage more beginning users!
73, Howard W6/G6LVB