You're effectively talking about an attacker breaking https aren't you? Unless you can detail another way to
get at a user's token. I'm curious to hear about it.
I did, and xss and session sniffing listed on the OWASP web page, would be prevented by following OAuth flows. So that just leaves mitm, which as I said, is effectively breaking https.
No. There are many ways to fish bearer tokens. Encryption in transit only addresses some of them.