I wonder when will be Typescript done, there is only so much that one can do adding a type system to JavaScript, without starting to become C++ like complexity language, which arguably already is.
It's already there. There are less and less new type features, all they do is implement any new ECMAscript proposals that made it to stage 3 at least. If you look at the changes of this and the last few releases, it's mostly internals, tooling and handling and other non-type things. Decorators are in TS 5 now because they made it to stage 3 last year.
They have to follow the other current and future ECMAscript proposals and implement them though, so new features to be supported has for quite some time dependent almost entirely on the ECMAscript process. On the pure TypeScript side there was only minor tweaking and small corrections (for example, TS 4.8 brought "Improved Intersection Reduction, Union Compatibility, and Narrowing", clearly not a new feature but improvements to an existing one).
Meanwhile tsconfig.json keeps getting bigger, with combinatorial explosion of Haskel like feature sets, regarding how a source file is to be understood.
At least we get lots of opportunities for interview questions.
