I’m not familiar with either, but Duck Duck Go suggests:
https://www.citrix.com/blogs/2015/12/09/using-lets-encrypt-for-free-ssl-certs-with-netscaler/
https://techdrabble.com/citrix/netscaler/18-letsencrypt-automated-certificate-with-citrix-netscaler
https://www.f5.com/company/blog/nginx/using-free-ssltls-certificates-from-lets-encrypt-with-nginx
Well AWS ACM already automates this, so if the renewal period gets shortened, I’m guessing that this will be updated to suit, unless I’m misunderstanding your point.
I hadn’t considered the CPU load, but that’s a fair point. I’m guessing that a suitable piece of code will utilise specialised hardware, or perhaps leverage the GPU or just in time SSL certificates will become a thing.