Thanks for reaching out and sharing the feedback. It does sound like a great feature request and I will share the feedback with the Engineering team and you can do that too by posting the request on our UserVoice Page(https://adobexd.uservoice.com/forums/353007-adobe-xd-feature-requests) to include this option in Responsive resize the panel.
Regarding Dark theme, we have already received a similar request on our UserVoice page and I'll request you if you can share your comments and upvote this request: https://adobexd.uservoice.com/forums/353007-adobe-xd-feature-requests/suggestions/12940362-dark-inte...
This is the best way of communicating with the Engineering and Product Management teams regarding issues and suggestions so they can be implemented in future releases.
Thanks. A proportional change of blocks is very often used on sites. It will be great if you add this feature.
Spaces that can be formed between blocks when changing an artboard can be removed by linking the upper blocks with the lower grouping.