was that since the rule change gold star alliance partner travellers could not reserve E+ in advance, but would be given priority to be seated there (in E+) on the day of departure on a first come/first serve basis (seemed to be airport based at time of check-in)

Since 29 such seats are available, according to another poster, that sounds like pretty good odds.

My information is based on my being EB gold (SK) and connecting through SEA
on my way to/from CPH both before and after the rule change. I think there were at least 6-9 flight involved. As I was often arriving after a long flight from a timezone 9 hours away, I never tried online checkin, so don't know how that may/may not be impacted.

Hope this helped.