Sure, and you can do that with Rust today. There's nothing stopping you from writing a custom data structure with its own custom allocator. The "abort on OOM" policy is not a property of the language, it's a property of certain collections in libstd that use the global allocator.
I think the point here is that users would like to use Vec, HashMap etc using that arena allocator and handle OOM manually instead of having to write their own collection types.
