He seems to be having fun again instead of needing to be so serious and boring and safe like in such a military grade C# implementation. So this seems waaaay more healthy for the old fella, to put some spring back in his step.
What I'd like to see is similar in nature to TS's type definition file, but be more generic/js-engine agnostic so you could feed it to a JS engine so near-perfect type information can be fed to Chakra to specialize the compiled code if possible so it emits a near-perfect high-perf compiled version that the actual code can then use as a prepared, now specialized run-time ready to rock whenever the code actually does run. Sure JS is dynamic but helping the compiler do it's job when it's not required can't be bad, its just being compiler friendly if it does add any value or benefit. Whenever it finally happens you can almost enforce run-time security when JS engines support function freezing in the VM since the templated types can have the freeze keywords where we intended them to be, helping the run time code stay unmodified and for its coded intention only.
Good to see this since I apparently missed it... and I can't wait to get some more juicy brain-food a-la-Charles.