lists should be backed by a data structure offering O(1)-ish append and prepend

[SethTisue]

on the JVM we use scala.collection.immutable.Vector for this

ClojureScript offers something similar, so at least one JS-based implementation exists. @qiemem has found ClojureScript's data structures packaged separately as http://swannodette.github.io/mori/

[SethTisue]

@TheBizzle curious whether this already happened, or whether there's still a prospect of it happening

[TheBizzle]

It hasn't happened, and I would guess that it's unlikely to. Performance is certainly an issue in NetLogo Web, but the problems run deeper here than just changing some data structures. I don't think plain JS can hope to be competitive. Currently, I'd say that hopes being pinned on an experimental version of NetLogo that is being written in Rust (and that compiles to Web Assembly), which has shown some serious promise.