> I understand go's reasons, ReDoS etc, but the "purism" of RE2 does fly in the face of practicality to an irksome degree.

Preventing ReDos is literally the reason RE2 exists though, so I don't think it's "purism" to not implement these things. What you want is not unreasonable, but fundamentally incompatible with the goals of RE2.

Ways to do look-behinds in linear time, as detailed in this article, are a relatively new development AFAIK(?) I don't think the RE2 people are principally opposed to integrating that if it can be done well. I suspect someone will have to write a patch though, since the main RE2 maintainer died last year.