Use-case: I work on a news site and I want to create visual transitions between articles, but I don't want to lose the benefits of streaming. So:

• User clicks on link
• Create a new article element to contain the incoming article
• Start fetching content
• Pipe content into new article element
• Begin the visual transition once elements appear in the new article element

Not only is innerHTML is slower way to do this (due to a lack of streaming), it also introduces a number of behavioural differences. It'd be great to try to limit these, eg allow inline scripts to execute before additional elements are inserted.