The "one pacific crossing" relates to each ticket - if I have 2 tickets, then I'm allowed 2 crossings. No rule is being broken.

The only 'rule' I can think of that someone might be trying to get around by having 2 (or more) tickets at the same time is the "minimum days away" rule. Some tickets (depending on class and origin) require you to be away for at least 10 days. Other than that, what rules are being broken if someone has more than 1 ticket active at a time? Why would any oneworld airline care - I assume they would appreciate the business, particular as the 'alternative' is presumably to buy a *A ticket? As RTW tickets have unlimited stopovers, many people "go home" part way through and then pick up the ticket again, either using a paid ticket home, an award ticket - or in some cases, by having multiple RTW tickets at the same time.