A downside is it makes the site unusable for screen readers and SEO, plus it adds backend costs (compared to a plain backend that serves static files) if it's g

A downside is it makes the site unusable for screen readers and SEO, plus it adds backend costs (compared to a plain backend that serves static files) if it's generated dynamically, although one can pre-generate a bunch of variants and randomly pick one at runtime (which could be handled by the load balancer) to minimize the costs.