From: "JimO"

In principle, couldn't qualified ESA 'Soyuz commanders' such as Reiter or
Haignere be the commander?

Of course, but I judge that to be politically untenable for the Russians
(Russian spaceflight with no Russian cosmonauts onboard!).

(I think both Haignere's are retired, but Fuglesang qualified, and I think
Duque, too).

Dave