> I think the problem is there is an existing paradigm of libraries allocating their own memory.

That is a problem, and the biggest reason for why the arenas proposal was abandoned. But if you were willing to accept that tradeoff in order to use the Go built-in arenas, why wouldn't you also be willing to do so for your own arenas implementation?

> If there was a paradigm of libraries not doing allocations and requiring the caller to allocate this wouldn't be such an issue.

I suppose that is what was at the heart of trying out arenas in an "official" capacity: To see if everyone with bespoke implementations updated them to use a single Go-blessed way to share around. But there was no sign of anyone doing that, so maybe it wasn't a "big miss" after all. Doesn't seem like there was much interest in collaborating on libraries using the same interface. If you're going to keep your code private, you can do whatever you want.