You could potentially use WARC instead of Tar as the appended container, sure, but that's a lot of complexity, WARC doesn't serialize the rendered page (so what is the greater 'fidelity' actually getting you?) and SingleFile doesn't support WARC, and I don't see a specific advantage that a Gwtar using WARC would have. The page rendered what it rendered.

And if you choose to require separate files and break single-file, then you have many options.

> surely you could host "warcviewer.html" and "warcviewer.js" next to "mycoolwarc.warc" "mycoolwrc.cdx"

I'm not familiar with warcviewer.js and Googling isn't showing it. Are you thinking of https://github.com/webrecorder/wabac.js ?