A few comments:
- There's a div overlap problem with the current design.
- Hiding the default H1 header:
- This is confusing for people (like me) who expect to find it in a consistent location.
- This creates a problem with the "Gadget-edittop.js" gadget (per my screenshot)
- I personally prefer a plain or default aesthetic for wikipages, for a few reasons.
- It makes it easier to edit the contents in both wikitext and visual editor.
- Aesthetics are subjective, which is part of the reason why the wiki communities have generally used a very simplistic styling. Aka "content is king". Any embellishments purely for aesthetic reason can hence be problematic - either distracting to a subset of users, or subjectively 'ugly' to a subset of users. Plain wikipages might be 'boring' (in some opinions), but they're not actively offputting.
- Photo:
- I don't think the current header photo (the building&landscape) is a good, because attendees will be inside most of the day, talking to people. People (and the projects they create) are the focus of the event, and not the location.
- It's also extra bandwidth to download on mobile, and attendees will likely be checking the page regularly in order to see the schedule, throughout the event.
Ping @Qgil-WMF for feedback. Hope that helps.