Not necessarily. Depends on what the mirrorless 1-series is designed for.
If they are going for high fps + smaller form factor (like an A9), I think that might be more for news reportage/journos than it would be for sports/wildlifers. In that case, you might be talking about the 1DX3 and 1 series mirrorless going to different users.
But if it's a dead knockoff of a 1DX3 without a mirror (spec and form factor wise), I think it would aimed at / priced at the exact same photographers as 1DX3. Sideline sports and wildlife folks would use either body in their high fps pursuits.
Unless you think a 1-series mirrorless means high res. I don't think anyone is expecting that. Canon firmly chucked the high-res specialist camera into the 5-series price point 5 years ago (presumably to sell more of them at a lower price point).
First off, they've never stated they were releasing a mirrorless version of a 1D this year, so Joules was incorrect right out of the gates.....lol. We're talking about the EOS R ii, which is nowhere close to the specs of the 1DX mark iii.
The mirrorless "high end" Canon has been said to be roughly 2 years away from being announced.
And as I truly believe, these are 2 totally different targeted user groups.