I'm wondering how this gets interpreted for RTW tickets, particularly where the buyer acknowledges that seats will be limited.

For example, consider city pairs that have less than daily service, such as QF's DPS-PER flight, which operates only on Wednesdays. Could one show up at Denpasar on a Saturday and insist on QF flying them to Perth on that day, claiming Rule 80/90? Or would QF not be within their rights to state that seats are limited, and the next available A/D/L seat is available on the following Wednesday?

If QF could do that (and it seems reasonable to me that they could), is it not an extension of that theory to say that AA could offer you its next available A/L seat from Dallas to Anchorage, and that seat happens to be 4 months from now?