I have had three open itineraries at one time. It is a good way to do multiple trips over a long period of time. Why should that be a problem?

Based in Oz, I'll go - say to North America on a xONEx ticket, get a return ticket to Oz, re-start the xONEx ticket, get another return to Oz and so on.

The only problem is keeping up to speed with what you are doing and managing accordingly.

Just remember that each stopover gives opportunities for taking another trip from that stopover point. And, the rules of xONEx allow changes to date/time without penalty.