i'm not sure i follow your logic. how does a poor data connection affect js execution?
if you have to do additional template fetching via follow-up async requests, sure. but if you serve the js & js-parsed/executed template in the initial request, then the only difference would be a synchronous reflow/paint for js (white page flash) vs streamed/incremental reflow/repaint.
If you can barely get 1 request through, it might take a long time before the JS will load and run, as it has to load completely before running at all.
maybe amongst HN (i swear by uMatrix & uBlock Origin), but the general public prefers their favorite websites not to be largely broken.
completely disabling scripting [rather that just disabling third-party script injection] is not a pleasant experience, even for the technical crowd. i already reluctantly have to whitelist CDNs which can track me across the internet.