These things still seem not easily customizable in AsciiDoctor. Some references:

• http://discuss.asciidoctor.org/Example-block-numbering-relative-to-sections-td4016.html
• https://github.com/asciidoctor/asciidoctor/issues/979

I don't think it's worth to go for a custom template (nor would I know how to do it). Let's keep this open and do it once nicely supported by AD.