This assumes all SPAs would ignore unknown parameters they see in the fragment part. Even if the SPA itself doesn't use "targetText", it could still try to validate the fragment and abort with errors on unknown data present.

Also, this would require the "targetText" parameter to live peacefully alongside other parameters. (That in turn would require there were a standard definition of "parameter" inside the fragment at all)

E.g, if Chrome encounters an url with an existing fragment, it would somehow have to combine this with its own targetText parameter and hope the SPA still understands the combined fragment.