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.