I suspect that ‘HTML 5’ made its primary contribution(aside from the canvas element, which is about the world’s least efficient framebuffer) in spurring an arms race among javascript engines such that it is now possible to duplicate the power of bare-metal programming on a 1.79 MHz 6502 (with some hardware sprite acceleration) and 2KiB of RAM on a contemporary computer of merely modest specs…
In theory, (while it would be vile) you could ‘implement’ an NES in any browser modern enough to support a 256x240 cell HTML table and twiddle cell background colors (or 1 pixel images of different colors stretched to fill the cell, if you feel horrid); it would just be…not fast… on a level that mortals cannot truly comprehend until the javascript benchmark wars began in earnest.
(speaking of 6502s and javascript; nothing says “plenitudo potestatis, I haz it” like executing code, in-browser, on a virtual model of a once-current CPU (model built from actual die shots no less. No mere instruction set emulation here…))
