> Currently go, npm, and haskell projects are supported.
Implicit here is that you're missing out on one of Nix' strengths—that being how Nix-lang is a lingua franca for every ecosystem with a presence in Nixpkgs. I've never written or even seen a line of Pascal, but it doesn't matter because of the 'package' abstraction. I can build and/or install a Pascal program the same as any other.
> With Typescript, you get the full power of programming — the ability to easily factor out variables, to connect and abstract functionality, to reuse code, to write tests.
Nix-lang also has these, it's just FP rather than imperative. (Except unit tests unless you include Hydra or something.)
> [Nix has tech debt, such as] the somewhat cumbersome and inconsistent CLI interface. The garn CLI is a fresh start.
Nix also has this in the form of the "new" CLI a.k.a. Flakes a.k.a. nix3.
On the whole, I can see this being useful to someone trying to convert their coworkers from NPM to Nix, but not all that impactful in the field of Nix UX improvements. Nickel and co. are where the good ideas are coming from IMO.