So, I believe there is at least one exception to the "no tokens inside of tokens" rule.
If you are using an event integration, the {{member.webinar-url}} token WILL work inside a calendar token.
I have confirmed this with ReadyTalk support and you sign up for this test event, you can see it in action.
na-sj07.marketo.com/lp/readytalkdev/ACMECorporationMeeting_RegistrationLandingPage.html
I wonder if there are any other expeptions?