Agreed. OpenSSL's BIO system is actually very nice and is one of the nicer things about the library. Removing it is short-sighted.
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.
For example: http://funcptr.net/2012/04/08/openssl-as-a-filter-(or-non-bl... is a blog post I wrote wherein I show how to use SSL as a filter. The only reason I use a BIO is to temporarily store the same data I just got from the network and have in an std::string... it's duplication.