I know this thread is prehistoric. But I just came across it while searching myself to see if any progress is being made on this. And I felt I had to correct something the OP said --just for the record:
We’re basically killing Hugo’s spectacular performance with Asciidoc which is much slower than markdown, because it calls out to a slow Ruby executable.
Asciidoctor is not the bottleneck here. I wrote a piece myself a while back, when I converted my site from Hugo + Markdown to Hugo + AsciiDoc and suffered similar slowdowns:
As part of that process, I ended up having to run AsciiDoctor ‘standalone’ on my site because Hugo was refusing to build it. And I found that AsciiDoctor was easily capable of converting a couple of hundred pages in a few seconds. Similar in speed to what I was previously seeing with Hugo’s build times and a Markdown site.
So, in my experience, the problem is not with Hugo alone [which we know can build sites lightning fast] nor with AsciiDoctor alone [which, in my test was equally nippy] but lies somewhere in the communication between Hugo and AsciiDoctor. There’s something in there that is slowing everything to a crawl.
Unfortunately, 5 years on from this original thread, I’m still finding that Hugo takes an age to build my AsciiDoc site. There doesn’t seem to have been any progress made at all on this. Which may be because the finger has [erroneously in my opinion] been pointed at AsciiDoctor as the culprit and so filed under ‘Someone else’s problem’ by the Hugo dev team.
Which, I suppose, does justify this bit of thread archaeology!