Yeah it's a perfect example of a one man OS and a one man browser! Shows it's technically possible.
I still think what-one-person-can-solo-recreate is an awful terrible gate to limit what software is acceptable by though!
I look at how quickly & how competently people can make interesting powerful software systems on the web, that they can share & that can connect people, and I am in awe. Prioritizing recreating the platform is so low on my list of priorities: it's this time to power for devs, new & experienced, that seems like the better goal. And here the web just trounces everything else.
With just vanilla and some basic html one can take a page & very quickly begin to make it dance, in all kinds of wild ways.
I can take someone with a couple days of programming & pair with them & in a couple hours we can write a user script to rewrite some kind of weird or suboptimal computing experience they're already having, show them how easy it is to modify & improve their life & the online things they go through. That power is just amazing, and that there is so much freedom under the hood to be creative & do great things: that's thrilling & exciting for us all.
Time to start: fast, but with deep reserves of capabilities one can always tap into: that's greatness. The web's power curve is so much more exciting than anything else I've ever gotten to share with newcomers to the field. Connecting newcomers to computing has never been better, thanks to the great & powerful web.