There are practical backward compatibility and security issues currently that prevent widespread deployment. I’ve been leaning into io_uring going forward because it is clearly the future and brings a lot to the table. It still can’t be used in many environments but I expect it to be mainstream in 2-3 years. Niche, but not for much longer.

Most software doesn’t properly use the old io_submit facility and that has been around for decades, despite the large performance improvements possible. Even when io_uring is widely deployable, most software won’t use it.