20 years ago, I bought an "open ended" ticket to Europe. Outbound fixed, return simply needed to be confirmed with a 72-hour notice and used within 1 year. (Required availability of course, but it was a medium/high economy bucket and I was able to get what I wanted.)

It was around $800 R/T in an era when one-ways weren't available at all (short of buying full-Y). The discount-Y fare with change fees, taking a guess on an exact return date about 10 months in the future, would have been $700-ish. So I was paying less than a change fee to have the flexibility, and it worked out well. I never see these fares advertised anymore ex-U.S., but maybe they still exist ex-Europe.

The availability of one-ways on most routes these days may have killed the need for them.