"How about an option to leave a "pointer" instead (or in addition)?"
Absolutely. It's a wonderful hack, Astaran, but it leaves out those who participated in a thread (but didn't start it), who have just as much interest in hearing about a moved thread.
And including them in the private message scheme (per Muhammad's suggestion) would help, but it still leaves out readers-along who ALSO wonder where a thread went.
Leaving behind a pointer ("This thread has been moved to....") solves everything very simply and elegantly for all parties, IMO.
JIM