I am a frame builder AMA

Have you looked at the Paragon Syntace dropouts? I think it's a rather elegant design, from an engineering viewpoint if not so much aesthetically, and the Syntace inserts give you some wiggle room on alignment. I used them on my ultracycling bike, and they haven't fallen off yet. Only real downside is you need to use some proprietary Syntace parts but they're reasonably widely available and not too expensive.