The main problem with common VMs for multiple existing languages is that often the semantics of the language are heavily coded into the VM. For example, Parrot's core opcodes mimic Perl's behavior of "Type coercion for everyone, the string "0" is false!" There are a lot of other issues as well, and while they are certainly solvable, the resulting VM would be very heavyweight. If you want to design a VM that runs multiple languages, often you have to design the languages around the VM.
A standard VM/Runtime specification for all the browser would be awesome. We got plenty of them; CLR, DLR, JVM, Parrot, etc. Can you imagine? I can see those mime types already: application/csharp, application/perl, application/ruby, application/IL.
Right, call me silly but I'm honoring the "Right-click->View Source" spirit here, I don't know about you but I feel more confortable knowing that my browser is downloading source code and compiling or interpreting than downloading some kind of binary to execute, even if you call it "intermediate code", "byte code" "almost-there-machine-code" or whatever, it's still binary stuff. I get your point though.
But. Flash isn't served as source, is it? And JS is often minified/obfuscated. Sure you can run that through a tool to get back the source (sans comments and long variable names) but you can do just that with MSIL bytecode too.
I agree with your conclusions, especially that it's telling what Google is not doing, but I have to object to your "This was the original intent" lede. Whose intent was that? Not Sun's in '95 or '96 with the JVM, which was all about Java. Certainly not Netscape's.
Multi-VM/multi-language beats multi-language-single-VM, indeed, but then you have problems such as the cross-heap cycle collection one I raised on this thread. No free lunch.
And anyway multi-language-single-VM was never any browser vendor's original intent. I had folks like John Ousterhout belatedly (early '96) pitching TCL, but smart enough to see that it wouldn't fly (John then tried pitching Tk for cross-platform widgets, but Netscape was already screwing up its platform -- no sale).
Mid-90s C-Python, TCL, Perl 4 then 5 -- none of these was ever intended to be wedged into any browser and kept up-to-date. Not by Netscape or Microsoft or any vendor of that era, and not in the 2000s either. MS put IE on skeleton crew maintenance. The Silverlight-era "DLR" (single VM for many languages) was much later and not browser-bound.
And, I noted that it was not intended for a multi-language VM ("not necessarily a single VM with many languages", to quote myself, which I guess could have been more emphatic in denying that a multi-language VM was intended; I sort of assumed everyone would consider multi-language VMs the new hotness and not something that would have been considered back in the early days of VM-based languages becoming mainstream).
I'm not sure we disagree (and I would obviously have to defer to your much greater knowledge on the subject, even if we did disagree). I could have been more clear in what I was suggesting was "the original intent".
Yes, I added language= at the start, but the default was JS and I had no particular intention to support other languages using one or more VMs. I see what you mean now, though -- thanks. Hope this history helps. It's less meaningfully intentional than you thought. More like blind future-proofing.
To me, through my own skewed historical lens, it looks like an admirable level of humility. So, good job.