So for the first paragraph, this seems to be severely problematic for any software where someone you know and trust and who continues to have a good relationship with you is no longer available. How important this is will obviously vary, but predicating some important benefit of the language and saying that this benefit won't cause issues in the future because you can "ask the maintainer" is pretty unrealistic for proprietary software.

For the second paragraph, that depends a great deal on (a) what the mechanism used to "send a (shared, ref-counted reference thing) to another thread actually means and (b) what objects are used to accomplish this. Certainly simply writing the address of a shared_ptr<T> in C++ will work out as you indicate. But that's not the only way to do it. Rust's benefit comes from you being "unable" to do it an unsafe way; C++'s benefit comes from the fact that somebody has probably implemented the safe way in C++ already :)