Trizek (WMF) What will talk page templates such as talk header and WikiProject banners look like in flow?
Topic on Talk:Structured Discussions
Same as they do now, only on the side of the page. See w:fr:Wikipédia:Forum des nouveaux/Flow for an example. All the things that would normally be at the top of the page (and you have to scroll past them to see any comments) are in a dedicated space on the side of the page.
@Whatamidoing (WMF) Would templates such as this and this be redesigned for the new layout? Also, what would the side panel look like on a mobile device?
In theory, templates are designed to be adaptable to any screen size. If not (fixed width, strictly sized elements), that's already an issue for the current talk pages. :)
In a perfect world, WikiProject templates that are posted on talk pages should be moved to another tab, to have only discussions on the talk page.
You can see the view of any Flow board on mobile by switching to the mobile view, like this: https://fr.m.wikipedia.org/wiki/Wikip%C3%A9dia:Forum_des_nouveaux/Flow If the screen is really narrow, the description goes on top of the page.