I'm using sd and am reasonably happy with it. Its only downsides are not quite being PCRE and not having the same syntax as sed, so it needs retraining and to be extra sure that it stays available in the places it's needed. The best part about sed is that it can generally be found in any *nix system.

I totally get that PCRE is a massive beast and might not be worth the effort. I would gladly settle for a smaller engine that can handle lookahead and lookback. Yeah, they're expensive, but they're powerful and convenient enough for me to still reach for them when I can.

Thanks for the consideration :-)