If you read this section, the author gets a lot of things right, but clearly doesn't know the space that well since there have been people building things along these lines for years. And making vague commentary instead of describing the nitty-gritty doesn't evoke much confidence.
I work on one such language/tool called mgmt config, but I have had virtually no interest and/or skill in marketing it. TBQH, I'm disenchanted by the fact that it seems to get any recognition you need to have VC's and a three-year timeline, short-term goals, and a plan to be done by then or move on.
If you're serious about future infra, then it's all here:
https://github.com/purpleidea/mgmt/
Looking for coding help for some of the harder bits that people might wish to add, and for people to take it into production and find issues that we've missed.
Mgmt doesn't care whether or not you want to build your system to be immutable, that's up to you! Mgmt let's you glue together the different pieces with a safe, reactive, distributed DSL.
Regarding your Talos comment, Kubernetes makes building things so complicated, so no, I don't think it will win out long term.