Yes, and BIOs are one of the parts that basically every major open source project uses:

Apache, Nginx, Node.js, curl, etc -- they all use the BIO API to provide TLS as a filter over their internal streaming APIs. Having personally worked on some of these projects, the current libtls API is not sufficient at all.

This isn't to say at all that OpenSSL's BIO API was great -- it could definitely use iteration all over -- and I hope libtls gets there, but it doesn't seem at all focused on realistic server workloads.