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Maven should stop producing "site", but it should keep producing "reports", and depending on report (as for example Javadoc is rendered by javadoc tool into HTML), render them into some "intermediate" format, like AsciiDoc or Markdown (w/ extensions) is. All All the legacy (now "exotic") formats (used nowadays by Maven only, for example APT, xdoc) should be dropped.
Most, if not all, of the site related things are completely neglected for 10+ years. Just accept that we have no manpower to maintain it. Bigger problem is wasted engineering hours spent on it (currently only 1 person works on all the site related stuff), as in 10 years perspective, all we can do is adopt to latest dependencies/libraries, remove usage of deprecated libraries, but even with these changes we will not get anything "more modern" or responsive site generation, on final output. IMHO, we should instead:
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