Solaris had kssl doing much more of this 7-8 years ago. In their case SPARC T1+ CPUs had hardware support to accelerate crypto ops but iirc kssl did not depend on it.

It also did not require applications to support/know about SSL/TLS. So after moving to Solaris 10 we were able to make some legacy apps use SSL/TLS without adding any code at all! Pretty cool stuff.

They did have a few vulnerabilities causing kernel panic that Snorcle had to fix - so in terms of adding more complexity to the kernel it's a risky approach but in our case it was totally worth it and it helped that the SSL/TLS traffic was all internal - nothing public facing.