Afaik many harnesses ship the "default" which is grep+read (like Claude Code). But I agree, IMO it's a weird gap. To be fair I don't think providers are that incentivised to reduce token burn at the moment, but my guess is that that will change and tools like this will become at least an natively supported option in some harnesses.
I would be surprised if, in the "mature" future of AI tools/products, the labs building the models are also selling/building to end users like they are now.
Would or wouldn't be? I think it makes sense that they will be because of the feedback loop on training. The lab generates tons of example text as part of the training run and if they have that using their own tools then the models will tend to prefer those tools.