This is kind of a 50/50 suggestion.

It's half useful because some people do review tickets they aren't familiar with some of the time.
It's half not useful because it's not productive to be sending a ton of Ajax calls to expand every thread.

Really the suggestion is right on the benefit and wrong on the solution. A far better approach would be doing something like "Print View" which re-renders the entire ticket to the browser in simple markup and without Ajax.

Ticket notes makes this irrelevant ;)

No longer relevant.