This is a good point, which I didn't get until your comment. I think they should surface this on that page, because it seems everyone is thinking this will be a big clash, but as you say, if someone shares a sentence, the likelihood is low.

To double check, does this means things like,

  https://www.spa/#!/path/to/view

Can become

  https://www.spa/#!/path/to/view&targetText=percent%20encoded

The only part I don't get about the likelihood and this extension is how it interacts with these kind of hash routes.

I haven't thought that much about the next part, but how do people feel about the following?

  web+text://https://www.spa/#!/route/to/view#targetText=percent%20encoded

or something. Rather than extending URLs vertically, extend horizontally into a different protocol the URI of which can encode the syntax elegantly.