Supposedly, the ability to change population between systems was for update 1 on the roadmap, but no update was made in that regard, and there is no mention for the next update. Where can we expect more control over population distribution?

It is planed for Update 2 as in this roadmap:
https://www.games2gether.com/endless-space-2/forum/65-general/thread/21182-endless-space-2-improve-list-updates-1-2-3-and-release