Originally reported by @pbokoc:

Docscii currently makes some attempt at preserving <indexterm>s, and it probably shouldn't, because:

• Most, if not all, of our books have barely or not at all maintained indexes, so they're barely if at all useful.
• Does ADoc even actually do indexes? Even if it does, there is none in the converted guide - we'd have to add it.
• Currently docscii converts indexterms with some weird rules, it gets in the way in the source and it makes asciidoctor/ccutil freak out with some nondescript warnings.

Before making a decision here we should probably talk to all writers - it's possible, if unlikely, that a book or two actually has a useful index that might be worth preserving.