I just finished spending bits and pieces of the past week tinkering with the new style system and creating new custom formats. I abandoned Scriv2 in part because the lack of styles made editing a bit of a PITA, and for a while wrote in Markdown, compiled to LaTeX or ePub on my own. When I saw Scriv3 released I promised myself to give it a go.
The current style system appears to be a game changer. It is a bit clunky when mapping to the ePUB/MOBI layouts, but that only took a few minutes to figure out by decompressing the ePUB to HTML and inspecting in Chrome. I would like to be able to set the HTML tags (not just the styles) for accessibility reasons, and wish it were HTML5 than XHTML; but I assume there are limitations using the ePUB format that would undermine my nits.
All this to say: thank you for styles. It is a marked improvement over Scriv2. Thank you for the new compile system; another marked improvement over Scriv2.