Hi, let me share some thoughts on the presented mockups:
- Article thumbnail: ok, but may be disturbing for experienced users that use the search for scanning the article text for syntax mistakes using insource and regexp search etc. As long as the thumbs are hideable by user css, it could be fine.
- Namespace tags: Please no, makes copying from the search results harder and breaks consistency. In the normal page title there are also no namespace tags, links are not displayed with namespace tags, ... Making it easier to distinguish between various page types may be somehow a global goal for MediaWiki, but I don't see why this should be forced only in the search results.
- Rearrange the sister search section: ok
- Collapse advance search: Please no. The advanced search is already collapsed, collapsing the collapsing switch again frees up just ~30px with almost no impact on the amount of search results shown as you can already see in the mockups. In expanded mode, it even takes more space as there is an additional collapsing toggle. It's unnecessary extra clicks and workflow interruption.
- Introduce a quick-view panel, Re-style metadata, New location for “create missing article”, Change the color of the “did you know” suggestion: ok