What this needs IMNSHO is guarantees that once the document is loaded it won't do anything funny.

My preferred approach is a 1. small subset of modern HTML and css 2. (optional) that can link to a common package of JS to do things like partial updates ans autocomplete.

Main point is: Once the page has loaded nothing goes on in the background unless the user is explicitly changing the document, i.e. regardless of how many such pages you open, your CPU quickly goes to 0 and stay there.

So this could work too.