During the development announcement of Canon EOS-1D X Mark III, Canon didn’t make all specs of EOS-1D X Mark III public. According to latest rumors on CR, at least two major features haven’t announced yet.
The first one is that Canon EOS-1D X Mark III will probably shoot 4K Video with PDAF and without crop.
The second one is that Canon EOS-1D X Mark III will be able to shoot 5.9K Video with external RAW recording.
And the IBIS is still not confirmed yet.
The image sensor of Canon EOS-1D X Mark III is expected 20.1MP as rumored before.