Rumours of a mirrorless 1DX level body have been around for a while. Since before the 1DX Mark III development was even announced, actually. But now according to a new report on Canon Rumors, it looks like it might actually be on the cards for 2021. They say that Canon “will definitely be announcing an RF mount mirrorless version of the EOS-1D X Mark III in 2021”.
Whether that means, a literal mirrorless version with pretty much the same specs and features or to replace what would be the EOS 1DX Mark IV is unknown, although it’s set to come in the second half of the year. CR has nicknamed it the “EOS R1” which I think would be appropriate, given the D1/D1X lineage.