I'm a bit split on this one.

Simple arenas are easy enough to write yourself, even if it does make unidiomatic code as the author points out. Pretty much anything that allocates tons of slices sees a huge performance bump from doing this. I -would- like that ability in an easier fashion.

On the other, hand, new users will abuse arenas and use them everywhere because "I read they are faster", leading to way worse code quality and bugs overall.

I do agree it would become infectious. Once people get addicted to microbenchmarking code and seeing arenas a bit faster in whatever test they are running, they're going to ask that all allocating functions often used (especially everything in http and json) have the ability to use arenas, which may make the code more Zig-like. Not a dig at Zig, but that would either make the language rather unwieldy or double the number of functions in every package as far as I can see.