Yea... the biggest and most stupid problem is that type info is used to develop to help prevent bugs etc, and all that type info during dev time is, lost in between over the wire, then reconstructed afterwards in the engines.... COMPLETELY redundant since type into is 92% used on both sides.
This may be a bad idea since it WOULD add more payload but IDE's and browsers should work together to make some type/function signature/forward declaration hinting script standard for the browsers to use, the same type info that devs use to code with, that way at least the type info wouldn't be lost over the wire for 0 reason.
This all depends on if the download size negates time spend parsing and optimizing without types vs with types provided in he engines. Basically a function signature definition include file to give all type info for the browser to use as the skeleton of all functions to help runtime without needing to do type checking & inference.
In my opinion types are being added as needed, and their almost always needed; sounds like the reasons standards bodies began in the 1st place, to standardize common practice for interoperability. So yes there seems like a need exists here in some way or another as long as its optional for compatibility and it provides a real boost in some way, might be interesting.