Insanely resource expensive, but still a very interesting "why not?" idea. I think a fitting use case would be adapting newer websites for them to work on older hardware. That is, assuming the new technologies used are not vital to the functionality of the website (ex. Spotify, YouTube, WhatsApp) and can be adapted to older technologies (ex. Google Search, from all the styles that it has, to a simple input and a button).
In theory this could be used for ad blocking; though more expensive and less efficient, but the idea is there.
So, it is a very curious idea, but we still have to find an appropriate use case.