In the end, it isn't that useful. I only routinely sign digitally to deal with the (Spanish) government, and they provide their own certificates and software to do that.
This is definitely not Stallman's take on "this", "this" being _OP's feelings_ or maybe how to deal with regret generally, not whether having children or not is or isn't a good idea.
Sure, but plenty of type systems are Turing complete. What makes this demo impressive is the (unique?) feature of string literal types and template literal types, which lets you operate on text (like, actual text, with no weird type-level encodings).
Well, certainly string literal types have been around in GHC Haskell for quite a while (7.10.x). They've also been a thing in Scala 2.12.x although the 'implementation' was some sort of weird type checker 'hack'. I believe Scala 3 supports them natively.
I can't speak to the ergonomics of actually implementing anything which uses them internally since I've never really had much use for them outside using the surface-level API of a couple of libraries.
Demos for a couple old versions: https://www.youtube.com/watch?v=NqKyHEJe9_w Demo for Pharo: https://www.youtube.com/watch?v=baxtyeFVn3w