Actually we can do split on AO-51. If anyone felt a DX-depition was worth the effort and resources, we just tell the DX to use one uplink channel and the people replying to use the other. It would maximise QSO rate and even a handheld with low audio would be Q5 without any interfering signals.
We considered doing this, but unless they used two receivers, how would anyone know when to shut up and when to call? Even though there is a capture effect, when 20 signals come up at once, usually no one wins. Now if we'd used the SSB receiver on the user uplink?
This whole DXpedition was on a space and operator available basis. We looked at sending a 817 for the transponder sats, but the space and operators unfamiliar with current satellites kept us to the HT and Arrow. I think it's still a positive that so many made QSOs considering the alternative.
Rest assured I've learned from this, and future efforts will benefit from those lessons. Meanwhile, I've identified the jerks among us from some of the really out of line negative comments directed at me and the expedition members ;-).